The industrial action will come in two waves later this month - first a four day strike from June 19, then a week-long stoppage beginning on June 29.

Employees of nine engineering companies voted for industrial action following a ballot among 9,000 workers.

Track maintenace workers are taking action

The walkouts, announced by the executive of the Rail, Maritime and Transport Union, are the latest step in a dispute over restructuring pay and conditions.

The RMT General Secretary, Jimmy Knapp, said there would be an immediate impact on services, that would get "progressively worse".

Railtrack, which is responsible for maintaining track and signalling, tried to reassure passengers with the promise of "contingency plans" but conceded services could be harmed.

"In the first instance it is expected that the impact will be minimal, it is difficult to predict the effects as the strike goes by," said a Railtrack spokesman.

The annoucement represents a double blow for rail industrial relations. Last week RMT announced its London Underground members would strike for 48 hours from June 14.

Commuters face major disruption

Mr Knapp said the engineering companies were asking for too many concessions, without offering enough additional compensation to his members.

"RMT has no problem with the principle for change but we are not going to be whipping boys while Railtrack and the maintenance companies walk away with massive profits," he said.

Tube workers have already planned a 48-hour stoppage

One of the engineering firms involved in the dispute, Jarvis, expressed alarm, saying they were already in discussion with the union and had agreed to negotiate without duress.

Nine companies, including a number of subsidiaries of major construction firms like Balfour Beatty and AMEC, carry out track and signal maintenance for Railtrack. The union says they made a combined profit of £300m last year.

Commuters in London are already facing the threat of disruption on the London Underground.