Workers on Southeastern trains in London are to be balloted for strike action in a row over jobs.
Members of the Rail Maritime and Transport union (RMT) based at Charing Cross and Victoria will be voting in the next few weeks.
The RMT said cutting the post of team leader had compromised safety.
Southeastern said the changes, already in place at two other stations, were working well and operational safety had not been compromised.
A Southeastern spokesman said: "The changes at Victoria and Charing Cross have been in place since December 5.
"These were already implemented months ago at Cannon Street and London Bridge following consultation with the RMT at these stations. The changes have worked well and have not compromised the safe operation of trains."
He added there would be no job losses but a change in the role of the people who currently hold the post of team leader.
RMT general secretary Bob Crow said: "Southeastern have been caught out yet again cutting staffing and operational costs to maximise profits in a move that will not only cause chaos on the platforms at Victoria and Charing Cross but which would also compromise safety.
"Southeastern have got the nerve to jack up fares by 13% while hacking back on platform operations that will delay and disrupt the dispatch process while putting their staff in the firing line as and when things go wrong."