The Government is set to announce an extended contract for Virgin Trains to run services on the West Coast Mainline, according to speculation.
Transport Secretary Chris Grayling is due to make a statement to Parliament on Monday about rail franchising.
The Transport Department and Virgin Trains made no comment ahead of the announcement.
But there is speculation that Virgin will be given an extension to run services on the West Coast for an extra year.
The franchise had been due to end in April, but the Government has previously announced that Virgin will run services until April next year before a new franchise was expected to be created to run the West Coast and HS2 services when the high speed line is built in 2026.
Any announcement of an extension to 2020 will be controversial, especially if other train operators are not able to bid.
Mr Grayling has been criticised for his handling of Virgin's East Coast franchise, which is ending in 2020, three years early.
The National Audit Office has announced it will investigate the Government's handling of the franchise, which is a joint venture between Virgin and Stagecoach.
Ministers have said any suggestion taxpayers would be out of pocket was wrong.
Mick Cash, general secretary of the Rail, Maritime and Transport union said: "Rumours are rife that Chris Grayling is setting up a major "market sensitive" announcement on the West Coast Mainline and that that announcement may mean a further cash-laden extension for Virgin and Sir Richard Branson without any competition or consideration of the public sector option.
"RMT awaits the announcement and after the fiasco of Chris Grayling and the Tory Party chairmanship just a few weeks ago we know that anything is possible with this shambles of a Government.
"However, if the well-informed speculation is correct it will expose yet again the cronyism and chicanery of the privatised rail franchising process and will ram yet another nail into the coffin of this whole rotten business.
"If the East Coast bail out is to be followed by a West Coast bung the British people will be rightly up in arms and it will reinforce the cold, hard fact that it's no longer a question of if our railways will be returned to public hands, it's a matter of when."
Lord Adonis, who stepped down last year as chairman of the National Infrastructure Commission tweeted: "Awaiting parliamentary statement about next Grayling rail bailouts at 5.45 - deliberately after the markets have closed. Prepare for another big row about Branson, Souter et al."