Uber is facing an employment tribunal claim from drivers who argue it is acting unlawfully by not offering rights such as holiday and sick pay.
The GMB union is backing two test cases which will also determine whether Uber drivers are entitled to receive a guaranteed minimum wage.
In addition, drivers are unhappy at pay being docked for customer complaints.
The GMB said that the case, being heard at the Central London Employment Tribunal, would have an impact on a further 17 claims that have been brought against Uber and wider implications for its tens of thousands of drivers in the UK.
It said the case was the first time that the company will have faced legal action in the UK over the issue of whether their drivers are classed as workers or are self-employed.
Annie Powell, employment lawyer at Leigh Day, which is bringing the case, said: "We will argue that Uber exerts significant control over its drivers in order to provide an on-demand taxi service to the public.
"If Uber wishes to operate in this way, and to reap the substantial benefits, then it must acknowledge its responsibilities toward those drivers as workers.
"We are seeing a creeping erosion of employment rights as companies misclassify their workers as self-employed so as to avoid paying them holiday pay and the national minimum wage."
GMB national secretary Justin Bowden said: "Uber drivers face very difficult working conditions and with cuts to fares we believe some of our members are taking home less than the national minimum wage when you take into account the costs of running a car."
Uber, which allows users to book and pay for a taxi by smartphone, says its more than 30,000 London drivers enjoy the flexibility of being able to work when they choose and receive on average more than the minimum wage.
The firm has grown rapidly around the world and is valued at $62.5bn (£48bn). The tribunal is expected to last until next week but judgment could then be reserved for several weeks.
It comes after Uber agreed in April to pay up to $100m (£76m) to settle lawsuits by US drivers over whether they should be classified as independent contractors or employees.
The case could have threatened the ride-hailing service's business model had the company lost at trial.
Theresa May faces two daunting challenges on the day she completes her first week in office as Prime Minister.
At noon, she faces Prime Minister's Questions, in the final session before the Commons rises for the summer recess.
And if Jeremy Corbyn is defeated by challenger Owen Smith, it will be one of only three PMQs in which she will face him, with just two more in September before the result of Labour's leadership election.
Immediately after PMQs the Prime Minister will head for Berlin for a working dinner with the German chancellor Angela Merkel, widely regarded as Europe's most powerful woman.
Mrs May's admirers have long claimed she is Britain's Angela Merkel, so their meeting will be studied carefully for the body language between them and any references to the comparison.
According to No 10, in what will be her first overseas visit as Prime Minister, she will aim to build relationships with partners across Europe as the UK prepares to negotiate its exit from the EU.
After Berlin, the Prime Minister will travel to Paris for talks on Thursday evening with President Hollande who, like Chancellor Merkel, is facing re-election next year.
During both visits, she is expected to hold one-to-one talks and try to establish personal relations that will pave the way for open and frank discussions in the months ahead as the UK negotiates to leave the European Union.
The Prime Minister is expected to repeat a point she made in early phone calls with these leaders: that it will take some time to prepare for those negotiations as the UK government consults with the devolved administrations and different industry sectors to determine what our objectives should be for that negotiation.
Speaking ahead of travelling to Berlin, the Prime Minister said: "I am determined that Britain will make a success of leaving the European Union and that's why I have decided to visit Berlin and Paris so soon after taking office.
"These visits will be an opportunity to forge a strong working relationship that we can build upon and which I hope to develop with more leaders across the European Union in the weeks and months ahead.
"I do not underestimate the challenge of negotiating our exit from the European Union and I firmly believe that being able to talk frankly and openly about the issues we face will be an important part of a successful negotiation.
"I also want to deliver a very clear message about the importance we attach to our bilateral relationship with our European partners, not just now but also when we have left the European Union.
"These relationships have been vital in the past and they will be vital in the future as we continue to work together to keep our people safe and to support economic growth that benefits people across our countries."
Government lawyers told a court in London on Tuesday that Mrs May had made it clear she did not intend to deploy Article 50, triggering the process of leaving the EU, before the end of 2016.
Downing Street, however, stressed that this was a decision for the Government to make.
:: Live coverage of Theresa May's first Prime Minister's Questions on Sky News at midday.
Those who wish to apply for a tick will still have to meet some criteria
Twitter's blue tick badge is to be made available to all users to "help people find great, high quality accounts to follow", the social network says.
The ticks are usually reserved for public figures but now an application form is available online for everyone.
An applicant will still have to supply various pieces of information and prove that their account "is of public interest" or that they have "newsworthiness or relevancy in their field".
They have to supply a verified phone number, email address, website and be tweeting publicly.
In a blog post announcing the new system, Twitter's Tina Bhatnagar said: "Our goal with this update is to help more people find great, high-quality accounts to follow, and for creators and influencers - no matter where they are in the world - to easily connect with a broader audience."
Twitter has around 320 million monthly users, of which around 187,000 are currently verified.
WikiLeaks has published 294,546 emails along with thousands of attached files from 762 mail boxes that allegedly belong to the primary email domain of Turkish President Recep Tayyip Erdogan's ruling Justice and Development Party (AKP).
The most recent email in the trove released by the whistle-blowing organisation on Tuesday was sent on July 6, 2016. The oldest dates back to 2010.
"It should be noted that emails associated with the domain are mostly used for dealing with the world, as opposed to the most sensitive internal matters," WikiLeaks said on its official website.
WikiLeaks said it obtained the emails a week before Friday's attempted coup.
"WikiLeaks has moved forward its publication schedule in response to the government's post-coup purges.
We have verified the material and the source, who is not connected, in any way, to the elements behind the attempted coup, or to a rival political party or state," the organisation said.
WikiLeaks previously claimed that the Turkish government would attempt to censor the distribution of the documents, and urged the Turkish public to be ready to bypass any government attempts at blocking access to the material.
"Turks will likely be censored to prevent them reading our pending release of 100k+ docs on politics leading up to the coup," the organisation said on Monday via Twitter.
"We ask that Turks are ready with censorship bypassing systems such as TorBrowser and uTorrent. And that everyone else is ready to help them bypass censorship and push our links through the censorship to come."
WikiLeaks later claimed that its infrastructre was "under sustained attack," following its announcement of the imminent publication of the AKP emails.
"We are unsure of the true origin of the attack. The timing suggests a Turkish state power faction or its allies. We will prevail & publish," WikiLeaks said on Twitter.
The Prime Minister will not start the formal process of divorcing the EU this year, the High Court has been told.
Government lawyers told judges considering a legal challenge over Brexit that Theresa May had made it clear she did not plan to trigger Article 50 before 2017.
The timetable was set out as a British hairdresser launched his case to try to prevent the Prime Minister starting the formal process of leaving the EU without putting it to the vote in the House of Commons.
Brexit campaigners have urged the Government to get on with it
Lawyers for Deir dos Santos, who is described as just an "ordinary guy", say Article 50 of the Lisbon Treaty should not be launched without an Act of Parliament.
His is just one of three cases being brought on the same issue - the law firm Mischon de Reya is bringing another on behalf of a group of clients and a third is expected from investment manager Gina Miller.
The High Court heard how the lawyers had been subjected to hate mail and anti-Semitic abuse since announcing their intentions.
Lord Pannick QC, instructed by Mishcon de Reya, told the court that publicity generated by the case "has provoked a large quantity of abuse directed at my solicitors".
"It is racist abuse, it is anti-Semitic abuse and it is objectionable abuse."
High Court Judge Sir Brian Leveson said the threats were being taken "very seriously" and warned: "The court will be concerned to deal severely with anyone who interferes in the course of this litigation."
Sir Brian said the case would likely leapfrog the High Court and be heard in the Supreme Court "not before the third week" of October.
He said the date would give the court sufficient time to consider the case before the Government considered triggering Article 50.
And added: "It would be extremely distressing if the Government were to say suddenly we'll just do it."
Brexit Secretary David Davis said last week that Article 50 should be triggered "before or by the beginning of next year".
The case, which has been described as the "most important in constitutional history", hinges around the wording in the Lisbon Treaty.
It states: "Any member state may decide to withdraw from the Union in accordance with its own constitutional requirements."
Lawyers say that decision rests with MPs - the representatives of the people.
African leaders have backed plans to deploy regional troops to South Sudan after recent fighting between rival forces left hundreds of people dead.
Soldiers for the African Union (AU) force are to come from Ethiopia, Kenya, Rwanda, Sudan and Uganda.
A 12,000-strong UN peacekeeping force is already in the country, but the AU force would have a stronger mandate, officials say.
South Sudan's government says it is opposed the deployment of the force.
"We are not ready for a deployment of even a single additional soldier," South Sudan's Information Minister, Michael Makuei Lueth, told the BBC's Focus on Africa radio programme. "That does not solve the problem."
President Salva Kiir and his rival, Vice-President Riek Machar, announced a ceasefire last week.
Clashes over several days between troops loyal to the two men had threatened a recent peace deal.
"The UN doesn't have the mandate to impose peace," the AFP news agency quoted AU Peace and Security Commissioner Smail Chergui as saying at the AU summit in Rwanda's capital, Kigali.
"They are there where there is peace to keep. African troops are ready to engage in very difficult situations."
He explained that the mission would be similar to the deployment of a 3,000-strong special force that took on the M23 rebels in the Democratic Republic of Congo in 2013.
Over the weekend, UN chief Ban Ki-moon expressed his support for the AU deployment.
But Mr Lueth blamed the recent fighting on the peace deal which, he said, was imposed on the country by regional mediators.
"As a sovereign state… this thing cannot be imposed on us without our consent," he said, adding that it would not "serve the interests of the people of South Sudan".
A new challenge for the AU: Analysis by Tomi Oladipo, BBC Monitoring Africa security correspondent
President Kiir will be hoping that the African Union shelves its plan to deploy troops in South Sudan as it did in the case of Burundi. So far the continental body has only sent forces in at the request of the state in need. Theoretically it can intervene against a nation's wishes, which is part of the remit of the new rapid-response African Standby Force.
The AU has a history of talking tough but so far has been unable to rein in problematic African leaders. It is also struggling to fund its operations - so taking on a new intervention force, reliant on external support, will only add to its challenges.
The AU wants to model this new force on the Force Intervention Brigade sent to eastern DR Congo to battle rebel groups. That was a collaboration involving the AU, the UN and the Southern African Development Community. The force defeated the M23 rebels after some 800,000 people had fled their homes during their insurgency.
Mr Kiir's troops make up the majority in and around the capital, Juba, contrary to the terms of the peace agreement with the opposition. So it would be a huge challenge for the AU force to attempt to call them to order, but it would provide a buffer to the outnumbered troops on Mr Machar's side, whose whereabouts following the recent fighting remains unclear.
Why did the fighting resume?
It seems a disagreement at a checkpoint between rival soldiers led to a shootout on the evening of 7 July in which five soldiers died. This quickly escalated into serious fighting the next day and over the following weekend.
Tensions have been high since April, when Mr Machar returned to Juba under a peace deal following a two-year civil war. He took a 1,300-strong protection force with him and they were supposed to start joint patrols with forces loyal to President Kiir. But a lack of trust between the two sides meant the patrols had not begun.
A ceasefire agreed last week is holding. But the two-year civil war started after clashes between rival soldiers in Juba and degenerated into nationwide conflict in which tens of thousands died.
The war was fought broadly between South Sudan's biggest ethnic groups - the Dinka, led by Mr Kiir, and the Nuer, under Mr Machar.
The international community played a major role in the creation of South Sudan and has tried to exercise some influence since independence in 2011.
The East African regional group, which brokered the peace deal, is behind the plans for a robust regional force to be deployed. Many foreign nationals have been evacuated because of the most recent unrest.
The African Union has launched a new passport. A lot remains unclear about the document but here is what we do know:
What is the African passport?
The idea behind the passport, which was launched this weekend, is for all African citizens to be able to travel throughout the continent without visas.
There are two passports - one issued by the African Union for officials and people who travel a lot on business, and the other by individual countries for everyone else.
It will bear the African Union's name and that of the issuing country.
Here is a diplomatic passport issued this week:
It is not known what a normal citizen's passport will look like.
Why have they been introduced?
It is an attempt to ease movement of people across the continent and stimulate trade across the continent.
These kind of blockages hinder inter-African trade, which remains very low.
Many countries still do more business with their former colonial power, than with their neighbours.
AU Deputy Chairman Erastus Mwencha told the BBC that the issue of free movement had been "on the table" for 25 years.
He believes that it is necessary for Africa to "harness" the talents, skills and labour of its population.
Who will get one?
At first it will be rolled out to African heads of state and top AU officials and foreign ministers.
The first recipients were chairperson of the African Union Idris Deby and Rwandan President Paul Kagame.
The ultimate goal is that all African citizens will be able to apply for an African Union passport.
However, this still depends on countries passing the necessary legislation in their own countries.
It is unclear if everyone who applies for a new passport will automatically get an African Union one or if you have to request one.
It is also unclear if everyone will have to update their passport before travelling or if people will still be able to travel with their old passports.
All the African Union has said is that individual countries will make their own decisions on issuing passports.
Which countries will get them?
All members of the African Union should get an African Union passport, provided they pass the legislation in their country.
This means every African country apart from Morocco - although Morocco has just asked to rejoin the AU.
When will people get them?
Some heads of state have already been given an African Union passport. The full roll-out for African citizens is supposed to happen by the end of 2018.
However, details of that roll-out are sketchy.
One interpretation is that the strategy is not clear because the passport has been rushed through before all the necessary arrangements have been put in place.
Will they be secure?
It is a biometric, or e-passport, that meets international standards and will be modelled on the European Union one.
Mr Mwencha argues that they will be more secure than the current passports that are not biometric documents.
The old passports, he says, are easier to forge. He told the BBC it will be easier to track criminals and terrorists.
However, with all countries able to issue the passports, that means a lapse in a single country could affect the entire continent.
Why not just change the visa system?
It isn't clear why a reciprocal agreement among all African countries to allow each others' citizens through their borders without visas wasn't made instead. It is possible that this may be seen as more secure.
The AU is also pushing for citizens of all African countries to be allowed to stay visa-free for 30 days across the continent, before the roll-out of the passports.
Will it actually happen?
AU Deputy Chairman Erastus Mwencha says not one country in the African Union has objected to the plan. So it only won't go through if parliaments block it.
But again, the details of the plan are sketchy.
However, many African countries might be reluctant to open their borders, fearing a huge influx of people from other countries.
This might be especially true of South Africa, which currently hosts large numbers of migrants from across the continent, and has seen xenophobic attacks.
Many argued that the passports should not be issued to the "elite" first.
While others complained that it would have been cheaper to have an agreement about visa-free travel and that there were more important things to worry about.
What other challenges are there to African trade?
A big one is travel infrastructure.
Many countries have more flights to London or Paris than with other countries on the continent.
For example, there are very few flights between Abuja and Dakar - two major West African capitals - and passengers sometimes have to travel via Nairobi or Addis Ababa in East Africa, or even Europe.
So even if the passport is introduced, a lot of work would still need to be done to make African trade easier.
