London Underground maintenance workers are planning a series of strikes in a dispute over safety.

The Rail, Maritime and Transport union is set to hold seven 12- or 24-hour stoppages beginning Feb. 12. Strikes are expected into June.

The union's general secretary, Mick Cash, says maintenance changes put into place by the subway's managers are "ill-conceived"

Steve Griffiths, chief operating officer at London Underground, says that safety is a top priority. He says there are "robust and comprehensive procedures" in place to make sure staff working on the tracks are safe.

Griffiths says that the underground will keep speaking with the unions about changes to the system.

A separate strike by station staff is planned for Saturday evening, lasting 48 hours.