Virgin Trains East Coast wants to replace its travel centres with open plan "customer zones", the Transport Salaried Staffs Association said.
Stations at London King's Cross, Edinburgh, Peterborough, Doncaster, Wakefield, Leeds, York and Newcastle could be affected.
The firm said it would consult staff.
The new "customer zones" would allow staff to advise and help passengers buy tickets through machines leading to the loss of 31 travel centre jobs and 15 station staff, the union said.
It said a memo had been sent to staff outlining the plans and that redundancies would be on a voluntary basis.
General secretary of the union, Manuel Cortes, warned of possible industrial action.
"This looks like another cost-cutting exercise at the expense of passengers and staff, all dressed up as improving customer service," he said.
"It looks to us it will mean longer queues and more expensive tickets because we have not yet got the technology to sell the whole range of tickets through hand held machines."
He said there appeared to be a "wider agenda of attacking staffing conditions across other franchises", citing the current Southern rail dispute over plans for drivers, rather than guards, to open and close carriage doors.
Mr Cortes said union members were "clearly unhappy" with the situation, adding a ballot on industrial action had not been ruled out.
In a statement, Virgin Trains East Coast said the proposed changes were part of "plans which put the customer at the heart of all our operations".
"Where any changes affect our travel centre colleagues, we will be consulting fully with them and the TSSA in due course," it added.
A rail company is planning to axe up to 46 jobs at travel centres and train stations along the East Coast Main Line route, a union has claimed.