An e-petition urging the government to reconsider changing the operator of the West Coast Mainline rail service has attracted more than 100,000 signatures.
The petition, on the Downing Street website, now has enough support to trigger a debate in Parliament.
The Labour MP in charge of the Commons transport committee has written to ministers asking them to postpone signing the contract for the service.
But the government has said the deal could be agreed as early as next week.
Virgin Rail lost its bid to continue running the line to rivals FirstGroup.
The e-petition, started by Ross McKillop, says Virgin has "delivered a reliable service for 15 years".
Once a petition has more than 100,000 signatures, the House of Commons backbench business committee must consider whether to grant time for a debate.
Liberal Democrat MP and party president Tim Farron tweeted "Now the @ Virgin Trains petition has reached over 100,000 I think we must debate the issue in Parliament."
The committee is expected to meet next on 4 September.
A Department for Transport spokesman said: "The Leader of the Commons will be referring this petition to the backbench business committee for consideration for Commons debate.
"The earliest contracts can be signed is midnight on Wednesday 29 August."
MP's concerns First Group, the UK's largest rail operator, will take over the franchise from 9 December and is set to operate the service until 2026.
The firm, which made the highest bid, has said it would bring in key improvements for passengers.
But Labour MP and transport committee chair Louise Ellman - whose constituency on Merseyside is served by the rail line - has sent a letter to Transport Secretary Justine Greening calling for "greater transparency to the process" and an opportunity for her committee to investigate what she calls "a number of concerns".The MP for Liverpool Riverside wrote: "This franchise will affect millions of passengers and last for up to 15 years. A great deal of public and private money is at stake.
"I have no fixed view on the matter and no preference for any of the bidders. My wish is simply to bring greater transparency to the process."
Public opinion FirstGroup said it would introduce 11 new 125mph six-car electric trains on the Birmingham-to-Glasgow route and provide more direct services between destinations.
The government says the new trains should add a further 12,000 seats a day on West Coast routes from 2016.
However, the petition says that Virgin "have delivered a reliable service for 15 years and turned the line around".
The signatories call for the government to "seek public opinion in these franchise bids".
"The government should look at more than the highest bidder - look what happened with G4S at London 2012," they add.
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