Union officials will today hold talks with administrators in an effort to save thousands of jobs following the collapse of delivery company City Link.
The RMT will meet with Ernst and Young aiming to prevent almost 3,000 job losses.
Ahead of the meeting in Leeds, the union said it would stay in talks for as long as it takes to prevent the job losses.
RMT general secretary Mick Cash said: "RMT's objective now is to do everything we can to rescue jobs in the wake of the shock collapse into administration of City Link on Christmas Day.
The union has also demanded urgent talks with Business Secretary Vince Cable, whom they called on to take an "active role" in the negotiations "right now".
Business Secretary Vince Cable has vowed to step in to help save nearly 3,000 City Link jobs after the company announced it had gone into administration.
The Liberal Democrat minister said he was keeping abreast of the situation and would meet union officials in the New Year to see if anything could be done.
However the future for City Link, one of the biggest parcel delivery firms in the UK, looks doubtful after John Lewis, one of its major customers, said it had transferred its business to another courier.
All City Link delivery services have now been suspended but customers can collect their own parcels from one of the many depots across the country.
A City Link worker who only found out his job was at risk on Christmas Day said he thought the firm was doing well.
The first Dean Bradshaw, like many others, heard of it was on the news.He said: "I wasn't sure if I was hearing right. I thought it can't be true.
"We're doing quite well, we've invested a lot into the company with new machinery and things like that. So I didn't think it was at all possible."
RMT Union general secretary Mick Cash called the timing of the announcement "disgusting".
ITV News Correspondent Richard Pallot reports:
Business Secretary Vince Cable has said the news of City Link being plunged into administration is a "bitter blow" for the parcel company's workforce.
In a statement the Liberal Democrat minister said:
This is a bitter blow to the workforce, many of whom have served the company loyally and now face huge uncertainty over Christmas. I have asked my officials to be kept abreast of any developments in this case and I will happily meet the union in the New Year.
The Shadow Business Secretary Chuka Umunna has tweeted his sympathy for City Link workers, saying he hopes a buyer can be found soon.
Nearly three thousand jobs are at risk at the Coventry-based delivery firm
1/2 Feel terribly for CityLink workers subjected to Xmas uncertainty. Its inexcusably cruel allowing things to reach this point at this time
2/2 I very much hope that a buyer can be found for as much of the City Link business as possible so the maximum number of jobs can be saved
The John Lewis retail group says it has transferred all its business with delivery company City Link to alternative carriers in response to the "regrettable news" that the firm has gone into administration.
Union leaders have vowed to do everything in their power to fight for the thousands of jobs put at risk with the collapse of City Link into administration.
Mick Cash, general secretary of the RMT union, said:
This is the bitterest blow any group of workers could receive on Christmas Day and it is absolutely shocking that the company have sprung this announcement once all the Christmas deliveries have been completed.
RMT will do everything within its power to mobilise a political and industrial fight to save the thousands of jobs that have been put at risk as a result of this shock announcement.
Around 2,700 jobs are at risk after one of the UK's biggest parcel delivery services companies fell into administration on Christmas Eve.
Coventry-based City Link is owned by investment firm Better Capital, headed by Jon Moulton, the veteran venture capitalist and it is understood to count John Lewis among its largest clients.
Professional services company EY have confirmed that they have been appointed as Administrators.
EY said it expected "substantial redundancies" over the coming days because no buyer had been found to save the troubled company.
Operations have been suspended at all its depots until Monday, when customers and recipients will be able to collect their parcels.
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The mother and stepfather of murdered schoolboy Daniel Pelka have both lost a Court of Appeal challenge to their life sentences.
Magdelena Luczak and Mariusz Krezolek were ordered to spend at least 30 years behind bars for killing four-year-old Daniel, who was beaten to death in March 2012 after months of being starved and mistreated.
They had argued their sentences were "excessive".
Daniel weighed just 1st 9lbs when he died, having been denied food, forced to perform punishment exercises, locked in a box room, poisoned with salt and tortured.
Rejecting their appeal at the court today, Lady Justice Hallett described Daniel's suffering and death as "heartbreaking".
She said the trial judge had been "fully entitled to treat this as one of the most serious offences of murder to come before the courts".
Krezolek had also appealed against his conviction, which was also thrown out by the appeal court judges.