Trainline has sued Labour's Transport Secretary Heidi Alexander over allegations she snubbed them by offering a £32million contract elsewhere.
State-owned London North Eastern Railway (LNER), which has been run by the Department for Transport (DfT) since 2018, was said to have recently extended a ticketing sales platform contract.
But the company did not offer rivals like Trainline the chance to bid for the 10-year-deal, it is claimed.
Trainline has alleged the failure to seek alternative bids means due process was ignored - as were the best interests of passengers and the taxpayer.
LNER reportedly awarded the contract for the central booking engine that supports its digital ticket sales to Australia's Vix Technology.
