The strikes, which are affecting Northern Train services across the North West as well as Southern rail, Merseyrail and Greater Anglia, are scheduled to take place across two days on Tuesday, October 3 and Thursday, October 5.
And train users are being warned to expect "extremely busy" rail replacement buses.
A spokesman for Northern Trains said: "To help keep our customers moving during the two separate days of industrial action on Tuesday 3 and Thursday 5 October, we aim to run over 1200 services on each strike day.
"The majority of available trains will operate between 7am and 7pm, with services on some routes finishing earlier.
"During these hours the overall number of trains running will be significantly reduced.
"We expect trains and any replacement buses we operate will be extremely busy.
"Please allow extra time for journeys, plan carefully and consider whether travel is necessary."
The RMT said the strike action would take place as part of their protest against Northern Rail's decision to introduce driver only operated trains.
Full details of the reduced services can be found on the Northern Rail website at https://www.northernrailway.co.uk/industrial-action