Merseyrail staff are planning to stage fresh strikes in the run-up to Christmas.
RMT members backed a motion to hold 24-hour walkouts every Saturday between November 2 and December 28 over driver-only operated trains.
Union members will also ban overtime on the network from November 3.
Previous strike action due to take place over the Bank Holiday weekend in August were averted by ‘positive’ discussions brokered by Metro Mayor Steve Rotheram.
But the RMT, which represents the 220 guards set to be affected by the new plans, claims that an agreement for a safe dispatch have been ‘scuppered’ by Merseyrail.
“It is with great frustration that our members have been forced to take strike action again on Merseyrail when we seemed so close to reaching an agreement on safe despatch,” said RMT general secretary Mick Cash.
“I want to congratulate our Merseyrail members for their steadfast resolve in this protracted dispute which is all about operating a safe service.
“Both the guards and drivers who operate the trains on a day-to-day basis are saying that they can’t accept the proposed method of operation and their voice needs to be heard.”
Merseyrail expressed their disappointment at the RMT’s decision to call for further strike action in the dispute, which has rumbled on since the end of 2016.
A spokesman said: “We are extremely disappointed that the recent exploratory technical workshops between the RMT, ourselves and Merseytravel have resulted in the announcement of further strike action.
“It is especially disappointing given that there is now a guarantee of a guard on every new train with a safety critical role and that we were so close to an agreement to end this dispute.
“Our priority now is to run the best possible service on the upcoming strike days and communicate the arrangements with our passengers as soon as possible.”