Workers who clean the Metro are to start a week-long strike, while cleaners at another rail firm are to be balloted for industrial action in separate rows over pay.
Members of the RMT union working on the Metro will walk out for seven days from Friday in a dispute which has already led to stoppages.
Meanwhile, RMT members employed by Arriva Trains Wales' cleaning contractors will receive ballot papers for industrial action over a claim for a pay increase and improved terms and conditions.
RMT general secretary Bob Crow said the union was stepping up its campaign for improved pay and conditions for cleaners on the railways.
– Bob Crow, general secretary of RMT
"This dispute is a mirror-image of all that is wrong in this country, with greedy company bosses on one side and low paid cleaners providing essential public services on the other."