GNER rail workers are being balloted about strike action that could hit services during the Christmas period.
GNER's owner has filed for bankruptcy protection in the US
More than 1,000 staff are voting about whether to take industrial action in a dispute over working hours.
The RMT union claims a deal over a 35-hour week had been broken by GNER. Union officials are now deciding on dates for the industrial action.
Owned by Bermuda-based Sea Containers, GNER provides trains between London and Edinburgh on the East Coast main line.
Last month, Sea Containers hit the headlines when it applied for Chapter 11 bankruptcy in the US.
The legal move protects the firm from its creditors and allows it to continue trading while sorting out its finances.
The group filed for Chapter 11 protection after deciding it could not repay its $630m (£339m) debts.
The RMT union said it had decided to ballot its members as the rail firm was now trying to tie its deal on the working week to job cuts.
Guards, station staff, booking-office workers and some train drivers will take part in the ballot.
GNER said it was "surprised and saddened" by the union's decision.
The union warned that the financial problems of owner Sea Containers was forcing the rail firm to "squeeze" the franchise for cash, but added it would not back any move to cut jobs.
"The company is simply refusing to talk to us in any meaningful way about what should be the straightforward implementation of an agreement for a 35-hour week on the basis of existing, agreed staffing levels," said RMT General Secretary Bob Crow.
"Instead, they are cynically attempting to use the 35-hour week as a cover for the imposition of staff cuts throughout the company."
He added that staff were already under pressure across the company as a blanket ban on filling posts had resulted in staff shortages.
However, GNER denied the plans for a shorter working week were anything to do with Sea Containers' problems.
"We are surprised and saddened that the RMT has chosen to ballot for industrial action, especially as we have been talking with the unions about a shorter working week for more than a year and making good progress," a GNER spokesman said.
He added that until the "surprise" news of a ballot the two sides had been on the verge of reaching agreements in several key areas.
"Talks are ongoing in other areas and we want to continue to engage in a constructive dialogue," the spokesman added.
The union will now meet GNER managers to discuss the situation on 6 December.