It will be the third strike on London Midland within a few days
About 100 conductors on London Midland Trains are to stage another strike in a row over Sunday working.
The Rail Maritime and Transport union said its members would walk out for 48 hours on 29 and 30 March.
RMT officials said it followed failure to break a deadlocked dispute involving former Silverlink staff.
London Midland, which brought in managers to cover for conductors in earlier stoppages, said: "We will run as many services as we can."
Trains were delayed or cancelled during the two strikes in the past week.
There was a reduced timetable with passengers travelling from Euston to Crewe or Birmingham New Street having to change at Northampton.
All other London Midland services through Crewe and Birmingham New Street were unaffected.
The union also announced it had asked the railways inspectorate to investigate allegations of safety breaches during the previous strikes, claims the company has denied.