LONDON (AP) _ More than half of train drivers and station guards were expected to stage a 48-hour strike against London's subway system next week after mediators said Friday that talks had collapsed.

The Rail Maritime and Transport Union has called for the strike to start Sunday evening; it was expected to cause widespread disruption on Monday and Tuesday.

Some 6,500 of the London Underground's 15,000 staff belong to the union, including about 60 percent of the 3,300 drivers and station guards. Recent strikes have failed to shut down the network in part because the engineers belong to two different unions.

The strike, the latest in a series that began more than a year ago, is over union demands for no compulsory layoffs or changes to employment conditions under plans to sell part of the 243-mile network to private enterprise.

The London Underground, known colloquially as ``the tube,'' carries more than 2 million passengers on weekdays.