More than 250 Govia Thameslink Railway (GTR) staff will be balloted for strike action in a row over ticket office closures. The workers are represented by the TSSA union, who are in dispute with Southern rail bosses over modernisation plans.

The union claims GTR, the parent company of Southern, will close 34 ticket offices and only 49 will open during peak hours, with 47 jobs being cut because of the changes.

"The GTR franchise has let down the travelling public and its staff and we would like to see it stripped off its franchise as soon as possible because it is no longer fit for purpose," said Manuel Cortes, the general secretary of the TSSA.

"Passengers may have to suffer short term pain to see a long term gain in the shape of new owners, hopefully Transport for London, if ministers start seeing sense."

The TSSA's two-week-long ballot will start on 19 August and the union said it would co-ordinated any strike action with its sister rails unions to "maximise the impact". The warning comes after station staff represented by the RMT union across the GTR franchise voted 70% in favour strike action.

The union claims GTR is threatening jobs, pay and safety with the reorganisation of its ticket offices. "The GTR franchise is in meltdown and not fit for purpose," said Steve Hedley, the assistant general secretary of the RMT.

"Not content with axing catering services, closing ticket offices and attacking the role of their guards they now want to threaten 130 station jobs and compromise the safety of both their and staff alike," he added.

The RMT's governing body, its national executive, is considering the strike vote. A spokesperson for GTR said: "We note that only one in four (26.9%) voted for strike action, with more than half of RMT station staff members ignoring the ballot.

"While disappointed we urge the union to stop this dispute and save our passengers and staff further pain by becoming part of the solution rather than the problem."

Peace talks between the RMT and Southern rail bosses failed on 15 August. The parties had been negotiating at mitigation service Acas.