The strikes add further misery for passengers as hundreds of services have been cancelled by Northern and Govia Thameslink Railway since new timetables were introduced on May 20.
Northern has axed 165 daily services until the end of July.
Areas affected include Manchester, Liverpool and Blackpool.
The dispute has been raging for over two years and now affects five train operators. The RMT insists guards on trains are integral to passenger safety, while Northern says cuts to staff will reduce the time spent at stations.
In the latest dispute, the RMT had called for last-ditch talks to resolve the Northern strike.
They claim that taxpayers and passengers, and not the company, were footing the bill for the cost of the industrial action.
The RMT said the franchise agreement signed by Northern and the Government meant Transport Secretary Chris Grayling could reimburse Northern Rail for “net losses arising from industrial action”.
RMT general secretary Mick Cash said: “By bankrolling Northern in this way Chris Grayling is seeking to prolong this dispute.”
