Strike action could hit London as engineers on Southern Rail are balloted for action over breakdown in industrial relations.
Rail, Maritime and Transport (RMT) union confirmed that it will ballot over 200 200 engineering members on Southern Rail’s train operations.
It said that representatives had been raising concerns "over a number of issues" with Southern Rail, and that they have been involved in "lengthy discussions" to agree a new roster.
It added: "Management ignored the wishes of our members and unilaterally imposed a new roster making a mockery of the negotiating process and agreed procedures."
Southern Rail have issued a project called Lean, which prescribes the time engineers should take on each job. The union challenged this, saying that no consultation had taken place.
While saying that the union is available for talks, RMT general secretary Mick Cash said:
RMT will not stand by while agreed policies, procedures and agreements are unilaterally ripped up by Southern and as a result we are now in dispute and will shortly begin a ballot of our engineering grades for industrial action.
Southern is a company intensively under the spotlight over its performance at the moment and RMT will not have our members scapegoated for failures at the top by outrageous and intimidatory demands to meet impossible work targets and through attacks on working conditions.
The union is in no doubt that the pressure on these staff to deliver impossible targets compromises safety in what is clearly a safety-critical environment.