Strikes over guards on trains are to start on Northern and Merseyrail next month, as the dispute that has wreaked havoc on Southern services spreads to other parts of Britain’s rail network.

Strike ballots from both Merseyrail and Northern (Arriva Rail North) showed more than 80% of votes backing strike action, ahead of moves to change the roles of onboard train crew. Conductors on Southern have been on strike repeatedly since last April.

The RMT union has called a 24-hour walkout on all three rail services for Monday 13 March.

Merseyrail has confirmed that new trains from 2020 will no longer require guards, although it has promised to redeploy all staff. Northern has not confirmed plans but is also expecting to bring in new trains, as early as 2018, where conductors will no longer be essential, or required to open the doors.

The RMT said it would step up campaigns to maximise political and public support in its fight for a guaranteed guard on Merseyrail and Northern services.

The RMT’s general secretary, Mick Cash, said the ballot results sent out a clear message: “The union’s position on driver-only operation [DOO] 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.”

He said the action would have been preventable if the companies had “listened to the union’s deep-seated safety concerns, had taken them seriously and had put passenger safety before profit”.

Merseyrail said that if strikes happened it would “work hard to provide the highest level of service possible”, including training managers to work as guards. It said, however, it was committed to continuing talks.

Jan Chaudhry-van der Velde, Merseyrail’s managing director, said: “Every industry needs to modernise, otherwise its future is at risk. The advanced technology on the new trains means they will no longer require traditional guards.”

A spokesman for Northern said: “As our modernisation proposals are still in the early stages it is a shame that RMT has announced strike action. We want to protect jobs and pay, and during our recent discussions we offered to consult fully with our people, customers and key stakeholders.” He said that customers could be reassured that a revised service would run in the event of a strike.

The further strike on Southern was announced after the RMT said its offer of talks had been “snubbed” by the Govia Thameslink Railway, the operating company.

A Southern spokesperson said: “This will be the 30th day of RMT strike action for Southern passengers and today’s news is clearly disappointing. We asked the RMT executive to suspend any further action when they met today so that talks could take place, instead they have chosen to put their members through even more pointless industrial action. They say they want to talk, but they are hell-bent on further strike misery and causing disruption and hardship to people’s everyday work and family lives.”

Southern said it ran almost 90% of services during the RMT’s most recent strike, on 22 February.

A spokesman for the Rail Delivery Group, which represents train operators and Network Rail, said: “Rail companies want to harness technology and smarter ways of working to give passengers a better, more modern service, and these coordinated strikes will cause nothing but needless disruption.”