Labour is calling on the Government to delay signing a new West Coast Mainline contract until MPs have had a chance to fully debate the deal.
Maria Eagle, the Shadow Transport Secretary, has said the decision to take the franchise from Virgin Trains and award it to FirstGroup should be put on hold until Parliament returns next week.
The politician said there were concerns over how the move would affect fares and levels of service.
More than 100,000 members of the public have signed an online petition against the decision, in a campaign supported by double Olympic champion Mo Farah, Apprentice star Lord Sugar and celebrity chef Jamie Oliver.
Virgin boss Sir Richard Branson has offered to run the line on a not-for-profit basis to allow Parliament time to debate the issue.