As the legal wrangling continues to delay the signing of the UK Government's £5.5 billion contract with the Aberdeen-based firm, Virgin called on it to come clean on its commitments over the lucrative Scotland to London route in a fractious dispute.
Tony Collins, chief executive at Virgin Trains, said: "So far we have had an interesting wish-list from FirstGroup but no firm commitments. Our customers and MPs would expect to know more about these before any contract is signed by the Government.
"In any event, our firm commitments are more extensive than FirstGroup's wish-list. It is time for Tim O'Toole [the Scottish firm's chief executive] to come clean and reveal the true commitments."
Virgin's 10-question challenge includes:
l Will there be any compulsory redundancies?
l Is the £350 million investment guaranteed or conditional on customer numbers?
l Are journey time improvements London to Glasgow and services to Preston guaranteed?
A FirstGroup spokesman said: "We won the bid fair and square and we are not about to replay it in public for the benefit of the loser."
The company has promised more services, lower fares, additional seats and revamped stations.
A Department for Transport spokesman added: "We maintain that the allegations by Virgin and Stagecoach are ill-founded and misconceived but cannot comment further on ongoing litigation."
Labour has called for the franchise deal to be delayed so MPs can scrutinise the detail. Despite the judicial review application, Justine Greening, the Transport Secretary, will be under pressure to give a Commons statement next week.