London's subway workers are planning more strikes in a worsening dispute over all-night train services.

The Rail, Maritime and Transport union says Tuesday that workers will walk out for 24 hours from the evening of Aug. 25, and again on Aug. 27. The action threatens to disrupt service for most of the week.

Workers have already staged two strikes in the past month to protest plans to start new weekend night subway, or Tube, services from September. Union members are unhappy over pay and schedule arrangements for the new services.

Last week's strike shut down the London Underground system altogether, affecting huge numbers of commuters.

London's Tube system typically handles 4 million journeys during a business day.