Hundreds of London underground rail maintenance workers are due to carry out a series of 24-hour strikes, starting this Friday, in protest over roster changes and outsourcing of work, Reuters quoted a rail union as saying today. About 750 union members will walk out from 0645 GMT, followed by stoppages every Sunday from Feb. 14, until further notice. Lines formerly maintained by Metronet will be affected -- all lines other than Piccadilly, Northern and Jubilee routes. Maintenance staff are protesting at the imposition of new rosters, breaches of agreements and the handing over of work to external contractors, the Rail, Maritime and Transport (RMT) union said. "(London Underground) have been hell bent on confrontation through their tearing up of the Signals Framework Agreement and through the unilateral introduction of new working practices which mean they can make people work what hours they like, when they like," RMT General Secretary Bob Crow said in a statement. "RMT members have said enough is enough by voting overwhelmingly for action." London Underground (LU) said 750 members of staff were going on strike over alterations to the shift patterns of 32 staff, adding it was "astonishing" the industrial action had been called when conciliation talks through ACAS were still ongoing. LU said it was trying to introduce a roster system to ensure engineering staff were always available when the railway is operating, and said contractors were used for specific work. "They should stop threatening industrial action at every opportunity, when all that will do is lose their members more pay," said Phil Hufton, LU's chief maintenance officer. The world's oldest underground rail system has been hit by a series of labour disputes in recent years including a 48-hour strike by thousands of drivers, station staff and maintenance workers last June over pay and jobs.