More than 2,500 employees at five companies which conduct maintenance work on the old British Rail system are understood to have voted for action in common with seven out of eight other firms where results have been declared.
The new votes for stoppages could mean delays and cancellations through most of the network. A national delegates' meeting on Saturday will advise the leadership of the RMT transport union on the timing and nature of action.
The first strike could take place on 16 June, although some companies have agreed to talks on pay and conditions, the issue at the heart of the dispute.
Leaders of the RMT predict an "overwhelming" vote for action by their 7,000 members at London Underground.
Tube staff are concerned that their terms and conditions will be undermined as part of the Deputy Prime Minister's plan partly to privatise the system. An RMT official said employees believed the scheme would result in "longer hours, lower earnings and fewer staff just as they have elsewhere".
The first action could take place on 11 June.Reuse content