The US parent of rail firm GNER is on the verge of filing for Chapter 11 bankruptcy protection.
Huge debts at its parent company have added to GNER's woes
Sea Containers, the passenger and freight transport business, said that it is unlikely to be able to pay a $115m (£62m) bond due up on Sunday.
The company was suspended from the New York Stock Exchange earlier this month and is in the midst of restructuring.
GNER, which runs intercity trains along the East Coast main line, may now have to cut up to 300 jobs, union RMT said.
The services connect London to Edinburgh via a series of cities and towns in the east of England and Scotland.
Chapter 11 is a US legal device that allows a bankrupt business to carry on operating and prevents creditors from forcing it into liquidation.
Terrorist attacks on London Underground, rising electricity prices and growing competition have all dogged GNER's operations.
And passenger revenues for the first 14 months of its franchise were £32m less than anticipated.
Earlier this year GNER lost a legal battle to prevent rivals Grand Central and Hull Trains Company from operating services linking East Coast towns with London.
Sea Containers has been able to slash its debts by $648m to $610m and has sold off its ferry operations in the Baltic.
Despite these drastic cutbacks, a company spokeswoman said it "would be very bold to say that we could pay off all the debt".