Guards on Southern Railway are to stage a five-day strike in the long-running dispute over their role.
Southern’s services have been hit by delays and cancellations for several weeks because of industrial action.
The RMT said it had offered a three-month pause to action if the company agreed to suspend its proposals for driver-operated doors and allow talks to take place.
“That request has been kicked back in our faces,” said a union spokesman.
“The union wrote to new Transport Secretary Chris Grayling asking for direct talks after he said it was a priority to sort out the chaos on Southern. That letter has been ignored.” Southern, owned by Govia Thameslink Railway, is planning to implement changes to the role of conductors on August 21.
RMT general secretary Mick Cash said: “This action has been forced on us by the arrogance and inaction of Govia Thameslink and the Government, who have made it clear that they have no interest in resolving this dispute or in tackling the daily chaos on Southern.
“Our fight is with the company and the Government, who have dragged this franchise into total meltdown.
“We share the anger and frustration of passengers and we cannot sit back while jobs and safety are compromised on these dangerously overcrowded trains.
“It is disgraceful that neither the company nor the Government are prepared to engage and are looking to bully through the extension of driver-only operation and the attack on the guards set for 21st August.
“They should wake up and get round the table now as an urgent priority.”