Rail giant Arriva is suing the government after it lost its bid to run the East Midlands railway franchise.
The firm, owned by Germany’s state-backed Deutsche Bahn, said it wanted more information on how the Department for Transport assessed the bids.
The move comes after rival Stagecoach, which was banned from rebidding, announced it was taking legal action.
The Department for Transport (DfT) said it had “total confidence” in its franchise competition process.
The East Midlands line operates trains between Norwich, Nottingham and Liverpool.
The DfT said in April that Dutch government-owned firm Abellio would take over the running of the East Midlands railway franchise for eight years, starting in August.
On Sunday, the DfT said it would “robustly defend decisions that were taken fairly following a thorough and impartial evaluation