Drivers who deliver goods for Argos are set to go on strike just days before Christmas in a dispute over pay.
The union said the three-day walkout from next Tuesday threatened "mayhem" for Christmas deliveries.
Argos said it had contingency plans in place and was working to prevent deliveries from being disrupted.
Members of Unite employed by Wincanton - a separate company - at a national distribution centre in Staffordshire are engaged in a dispute over holiday back pay.
Unite regional officer Rick Coyle said: "This strike by our members will cause havoc and mayhem to deliveries to Argos shoppers in the run-up to Christmas.
"There will be a lot of very unhappy Argos customers, if they don't receive the iPhones, TVs and white goods that they have ordered as presents for relatives this Christmas."
He said strike dates were only being announced as a last resort and that "Unite's door is open 24/7 to try and settle this long-standing dispute".
Argos said: "We would encourage both sides to keep talking with the aim of coming to a swift resolution.
"We also have contingency plans in place and can reassure customers we're working hard to ensure this will not impact our deliveries this Christmas."
The strike adds to the industrial chaos in the run-up to 25 December with hundreds of thousands of passengers being hit by action on the Southern rail network and Post Office workers planning a walkout next week.
Unite said the dispute centred on how holiday pay is calculated after legal cases established that overtime and extra shift payments should be taken into account.
It said managers at Wincanton had offered to backdate additional pay to April, while it maintains this should go back at least two years, and that each driver is owed an average £700.
Wincanton said: "We are disappointed with Unite's announcement given that at Unite's request we already have a meeting scheduled tomorrow morning with ACAS to resolve the issue."
It said it had already agreed to change holiday pay calculations in a way that exceeds its obligations in line with recent rulings and guidance.
The company added that it was committed to ongoing dialogue with the union.
Donald Trump has postponed a long-awaited announcement on plans for his business interests when he becomes US President.
The President-elect has been under pressure to step away from his sprawling property and licensing empire to avoid possible conflicts of interest.
He had been due to detail his plans on Thursday - in what would have been his first news conference since winning the White House on 8 November.
Mr Trump hinted at his intentions last month when he tweeted: "While I am not mandated to do this under the law, I feel it is visually important, as President, to in no way have a conflict of interest with my various businesses.
"Hence, legal documents are being crafted which take me completely out of business operations. The Presidency is a far more important task."
In a TV interview on Sunday he repeated an earlier suggestion that he will hand day-to-day control of the Trump Organisation to his three older children.
He told Fox News Sunday: "Essentially, I'm not going to have anything to do with the management.
"When I ran, everybody knew I was a very big owner of real estate all over the world.
"I mean, I'm not going to have anything to do with the management of the company. I'm not going to be doing deals at all."
Mr Trump has faced questions over his holdings, which include hotels, golf courses, a business licensing the Trump name for use around the world and royalties from the television show The Apprentice.
No new date has been given for the news conference, but it is due to take place at some point in January.
Spokesman Sean Spicer said the announcement was being delayed so the President-elect could focus on recruiting his Cabinet.
He said: "With so many iconic properties and successful entities, moving the announcement to January ensures the proper protocols are put in place so his sole focus will remain on the country and achieving his ambitious agenda."
Meanwhile, Mr Trump tweeted that he would finally be naming his choice for secretary of state on Tuesday - with ExxonMobil boss Rex Tillerson tipped to replace John Kerry as America's top diplomat.
Mr Tillerson - who has worked closely with Vladimir Putin on oil and gas exploration - could be a controversial nominee at a time when US intelligence sources are accusing Russian hackers of intervening on Mr Trump's behalf during the election campaign.
The top two Republicans in congress - Mitch McConnell and Paul Ryan - have risked the President-elect's wrath by backing calls for investigations into the alleged attacks.
Philip Hammond says the UK's future relationship with the EU may not be fully determined by the deadline for Brexit.
The Chancellor told MPs there is an "emerging view" among businesses, regulators and some politicians that the two-year timeframe after Article 50 is triggered may not be long enough to reach a "clear and firm end state".
Giving evidence at the Treasury Select Committee, he suggested a transitional deal may be required to prevent a sudden "cliff edge" change in trade arrangements which could cause financial instability both in the UK and across the continent.
"Having a longer period to manage the adjustment between where we are now as full members of the European Union and where we get to in the future as a result of the negotiations that we will be conducting would be generally helpful, would tend towards a smoother transition and would run less risks of disruption," Mr Hammond said.
Article 50 is the formal process for leaving the EU, and Theresa May has promised to invoke it by the end of March 2017 - sparking a strict two-year countdown for the UK to negotiate a settlement with the trading bloc.
The business sector and the City in particular have expressed concern about what would happen if this deadline was missed, especially if the UK also quits the single market.
Mr Hammond's remarks follow a leaked memo that suggested Brexit Secretary David Davis was "not really interested" in a transitional deal.
A spokesman for the Department for Exiting the EU insisted the document did not "properly reflect" his views or Government policy, and added that Mr Davis was "looking at all options" to deliver a smooth and orderly departure from the European Union.
Stephen Kinnock, a Labour MP who supports the Open Britain group campaigning for a "soft Brexit" deal, described the Chancellor's acknowledgment that a transitional deal may be required as "encouraging".
He added: "There is a growing consensus that agreeing a new trading relationship between Britain and Europe may take much longer than the two years specified by Article 50.
"Not signing a transitional arrangement would mean punishing tariffs which would hit British businesses and raise prices in the shops."
Transport Secretary Chris Grayling has told striking Southern rail staff to "get back to work" and end a "completely unnecessary" dispute.
Hundreds of thousands of commuters faced the worst rail disruption in decades this morning as three days of strikes began on Southern, which runs trains linking parts of Kent, Surrey, Sussex and Hampshire with London.
Members joined picket lines outside deserted stations at the start of the 48-hour walkout, with another strike planned for Friday, as commuters took the day off, worked from home or attempted to drive, cycle or get the bus to work.
Single mother Jennifer Lehane, from Croydon, emailed Sky News a copy of a letter she had written to her MP on a bus "with tears streaming down my face".
She attached a photo of her six-year-old son "in his pyjamas with his blanket walking down the road" to school at 5.30am - two hours earlier than usual "so I don't lose my job".
She said all those involved in the dispute should "hang your heads in shame!"
Skills shortages and the UK's looming divorce from the EU mean hiring optimism among private sector firms is at its strongest for three years, according to a report on the UK's employment outlook.
The survey of 2,100 firms - by employment firm Manpower - found construction and utilities firms were most bullish on employment prospects for the first quarter of 2017, despite general uncertainty over the country's future relationship with the bloc.
It suggested a rush for talent was under way ahead of potential Brexit barriers.
The study said the skills shortage was particularly acute in the building trade, with scaffolders and bricklayers being paid up to £24 an hour.
Housebuilders shed or lost many key personnel abroad when work dried up in the UK after the financial crisis.
The shortage of skilled tradespeople has been cited by the industry as a factor behind the slow recovery in building to help ease the country's housing crisis.
The report said the biggest headache for employers was a shortage of suitably skilled workers, especially if Brexit makes it harder to recruit staff from other countries.
The report found hiring in the public sector was expected to fall during the first three months of the new year as budgets remained constrained.
Mark Cahill, Manpower's UK managing director, said: "UK companies are going into 2017 hungry for top talent.
"Employers are still unsure about what exactly Brexit will mean, but are not letting that uncertainty deter them from hiring.
"Some employers may be looking to bring in talent while they can before any curbs to freedom of movement across the European Union come into effect, as more than half of all the jobs created by UK employers this year went to EU workers."
Residents and aid workers trapped in Aleppo are describing desperate conditions with streets "full of dead bodies" as the Syrian army comes close to regaining full control of the city.
President Bashar al Assad's forces, backed by Russia, have recaptured large swathes of the city in recent days and, according to state TV, it now holds 98% of neighbourhoods previously occupied by rebels.
A Syrian military source said government forces and their allies are in the "last moments before declaring victory", while the head of the government's Aleppo security committee warned rebels they "either have to surrender or die".
Lieutenant General Zaid al-Saleh added: "The battle in eastern Aleppo should end quickly. They (rebels) don't have much time."
Residents sent texts, tweets and videos to make dramatic appeals for help or say goodbye, as they said they feared they would die or be arrested by government troops.
Abdulkafi Alhamdo, a teacher turned activist, posted a "last call" video on Monday, calling the crisis in the city "the most horrible massacre … in our history."
With rain in the background, Mr Alhamdo struggled to fight back tears as he described the devastation.
"Just yesterday, next door all the building collapsed and many people were killed," he said.
"You might not understand what we are suffering here."
"We wanted freedom, we didn't want anything else but freedom.
"I hope that something can be done and that we can leave and that we can speak together once more … I hope you can remember us."
Another resident, Monther Etaky, told Sky News that life in the city "is like hell".
A knifeman who reportedly stabbed a rail passenger at a train station in southeast London shouted, "I want to kill a Muslim", according to a witness.
One man was injured in the attack at Forest Hill station at around lunchtime on Monday.
Eyewitnesses described the "horrific" attack and its aftermath on Twitter.
One person wrote: "The perpetrator is currently ranting on the streets. Beware."
Another tweeted: "#foresthill The attacker shouted " Who is Muslim, I want to kill a Muslim approached the guy sitting with his wife on the 1st carriage."
Shellby Curry, 24, was with her one-year old child when she saw a man "waving what looked to be a knife in his hand" near the station and screaming words like "Muslims f****** hate them, kill them all".
"I was walking along and someone stopped and said 'be careful, he's got a knife'.
"As I looked around there he was. I just grabbed my baby and ran across the road. Looking back (I saw) him marching up and down waving his arm about."
Miguel Oliveira, 36, said he came "face-to-face" with the attacker, who he described as "shouting uncontrollably".
"He was walking towards me and he was shouting stuff like 'Death to Muslims' and 'Go back to Syria'," he said.
British Transport Police said the incident was not being treated as "terrorism-related".
A spokeswoman said officers were sent to the station after reports of a serious assault at 1.18pm.
"One person has been arrested following the incident and is currently in police custody," she said.
"One man was treated by ambulance staff at the scene and is currently en route to hospital."
