The union has been fighting the further extension of driver-only operation on the Southern network by Govia Thameslink Railway since April 2016, and has called a number of walkouts.
It has instructed RMT members on a number of rail franchises across the country, including those working on Southern services, not to book any shifts on Wednesday November 8 or Thursday November 9.
Both the RMT and GTR have organised a number of talks since the dispute started, but a deal has yet to be reached, with the union raising safety and access concerns with the extension of DOO.
Mick Cash, general secretary of the RMT, said: “Every single effort that RMT has made to reach negotiated settlements in these separate disputes with the different train operating companies over safe operation and safe staffing has been kicked back in our faces and we are left with no option but to confirm a further phase of industrial action in early November.
“It is frankly ludicrous that we have been able to negotiate long-term arrangements in Scotland and Wales that protect the guards and passenger safety but we are being denied the same opportunities with rail companies in England.
“This suspension of normal industrial relations by the employers has to end if we are to make progress towards a solution that guarantees safe rail travel for all.”
A spokesman for GTR said: “We are very disappointed by this unnecessary RMT strike action and the union’s continued refusal to engage with us in modernising the railway. We expect to run a normal service on most of our routes during the RMT strike days.
“Modernisation is urgently required to make lasting improvements and increase capacity on this, the busiest part of the UK railway, where passenger numbers have doubled in 12 years. As well as better infrastructure and new trains, we have updated working practices to make the most of new technology and improve services for passengers. The RMT needs to play its part if passengers are to benefit from service improvements.”
Last week the rail operator reached a deal with the leadership of train drivers’ union ASLEF over pay and conditions for those working on Southern and Gatwick Express services.
ASLEF members will now be balloted on the deal.
A Department for Transport spokesperson said: “The RMT is playing a political game, however it has backfired as Southern will be running more than 90 per cent of services for passengers.
“The RMT’s dispute is not about safety, as the independent regulator has ruled that driver-controlled trains are safe. No one at Southern is losing their job or any pay as a result of the changes being put in place.”