Disputes over the role of train conductors has spread to another rail company as more workers vote on whether to strike.
Members of the Rail, Maritime and Transport (RMT) union at Merseyrail received ballot papers on Friday and are being urged to back a campaign of industrial action.
Union members at Arriva Trains North started voting on Thursday in a similar dispute, while the RMT is embroiled in a long-running dispute with Southern Railway, where the role of conductors has already been changed.
RMT general secretary Mick Cash said: “The union’s position on driver-only operation is perfectly clear. We will not agree to any introduction of DOO and will fight to retain the safety-critical role of the guard and to keep a guard on the train.
“RMT has asked Merseyrail to give the union assurances that any new trains will have a second safety-critical crew member on board and that the guard will be retained on all services.
“We set out clear deadlines giving the company ample time to give those assurances but the company have flatly refused to consider a guarantee of a second safety-critical person on the new trains.”
The Arriva and Merseyrail ballots will close at the end of the month.
RMT members on Southern will strike on February 22.