The Rail, Maritime and Transport union, Aslef and the Transport Salaried Staffs' Association fear higher pension contributions for thousands of workers.

They claim many of the over 100 schemes for rail workers are in deficit. They want a 10.5% staff contributions cap.

Network Rail, which has the biggest scheme in the industry, said it was in good order.

It said talks would continue with the industry about future funding arrangements.

The dispute involves all the train operating companies and engineering firms which maintain the railways.

The unions, including the Confederation of Shipbuilding and Engineering Unions, launched a campaign on Monday aimed at protecting pensions.

It will involve nine regional rallies in Cardiff, York, Glasgow, Edinburgh, Birmingham, Bristol, Perth, Manchester and London.

'Deficit of millions'

The unions say that since privatisation a decade ago the number of pension schemes has grown from one to 101.

But there is a deficit of up to £600m and some workers could see their contributions double without an agreement with employers, the unions say.

"Unless a way forward is found soon, workers could be faced with an increase in contributions which will amount to a very significant cut to their take-home pay." - Brendan Barber, TUC general secretary

RMT General Secretary Bob Crow said some workers would face contributions of 21% of their salary when legal changes to schemes were introduced in July.

He said the clock was ticking towards industrial action this summer, according to BBC labour affairs correspondent Stephen Cape.

A stoppage could be the biggest in the industry since the 1926 General Strike.

The unions say they want talks with the government over capping contributions, combining the large number of schemes into just three, and keeping schemes open to all workers.

Ballot threat

"If employers and the government continue to respond in a negative way there will be no alternative but to resort to industrial action," said the general secretary of the TSSA, Gerry Doherty.

"If this is not resolved, we could see a ballot for strike action, coordinated by all unions in the industry."

The last national rail strikes brought the network to a standstill in 1994 when signal workers staged a series of walk-outs.

TUC general secretary Brendan Barber has written to Transport Secretary Alistair Darling to request urgent talks to resolve the issue.

"Unless a way forward is found soon workers could be faced with an increase in contributions which will amount to a very significant cut to their take-home pay," he said.