Train company GNER has launched a legal challenge against the decision to allow a rival operator to start services on the East Coast Main Line.
GNER says Grand Central has an unfair price advantage
It has applied for a judicial review of the Office of Rail Regulation's (ORR) decision to award access rights to new company Grand Central.
GNER claims the ORR's decision - announced in March - was unlawful and creates unfair competition.
Grand Central is due to start services from Sunderland to London this winter.
'Level playing field'
GNER says Grand Central's entry into the market is unfair, as its new rival will not have to pay as much track access charges.
A High Court judge is expected to hear GNER's claims in July.
GNER is also challenging the need for Grand Central to stop at York, which is already served by 61 trains a day to and from London.
"We welcome competition as it encourages us to keep improving, but competition should be on a level playing field," said a GNER spokesman.
GNER has run East Coast Main Line services since 1996.
An ORR spokesman said it would vigorous contest the judicial review.