Virgin Trains has launched a legal challenge in an attempt to hold on to its West Coast Main Line franchise.
Earlier this month, the company lost out to FirstGroup in a bidding war to run a new 13-year West Coast franchise from December.
Virgin boss Sir Richard Branson has reacted angrily to the decision, branding the bidding process "insane" and threatening to end all involvement with the railways.
Virgin, which has operated the West Coast line since 1997, said it was "commencing court proceedings" over the Government's decision to press ahead with the deal.
Transport Secretary Justine Greening is due to sign off the contract tomorrow. But Virgin is now hoping that its legal challenge will delay the signing.
Sir Richard has expressed concerns that FirstGroup will not be able to live up to its financial and service-providing targets for West Coast, which runs through the North West.