Union leaders have laid tracks for more industrial action on the Tube after the Rail Maritime and Transport Union (RMT) called a strike ballot among its 2,500 members.
The Transport Salaried Staffs Association said its members will vote on whether to strike in a row over safety and staffing levels with London Underground.
Its workers will vote between 15 February to 11 March, but the RMT has not yet set a date for the strike.
Gerry Doherty, RMT general secretary, said: “Despite the sound of certain people jumping on political bandwagons, this is a straight forward industrial dispute which we hope to resolve with London Underground through normal negotiations.
“We now have a window of opportunity to do just that. Industrial action is always the last resort. I am confident that our members will support us if that is what is needed to resolve the dispute, but the ball is now firmly with London Underground, ” he said.
Transport for London (TfL) said threats of strike action were “completely unreasonable”.