Cleaning workers employed by Vinci on London Overground struck on 5-6 April, demanding a wage increase to the London Living Wage of £10.55/hour.
Currently the workers are paid £10.02.
The workers were previously employed by Carillion, and were transferred to Vinci when their previous employer went bust.
Vinci has refused to offer them a pay increase.
Rail union RMT, which organises the workers, is also demanding that the cleaners now be brought in house and employed directly by Arriva Rail London, the train company that operates London Overground.