The RMT conference agreed on Tuesday to ballot 18,000 workers over plans to transfer signals and maintenance work in Merseyside to Merseytravel.

It claimed this could be adopted across the country leading to the industry's fragmentation and privatisation.

Merseytravel, run by local authorities in the North West, said it is about "investing in and improving services".

The firm is seeking talks with the RMT.

Network Rail took maintenance work back in-house last year but plans are now being drawn up to transfer infrastructure maintenance to another employer.

"This is a guinea pig for train operating companies to run their own infrastructure" - Bob Crow, RMT

The union said it feared the move would lead to maintenance work being outsourced to train operator Merseyrail, which would affect the terms and conditions of workers.

RMT General Secretary Bob Crow said it "beggared belief" to think maintenance work would go back to private operators.

"Merseyrail want to run signalling as well as operation. Some people will argue it is only a small operator so it doesn't matter but this will be the forerunner for the whole country," he said.

'Local solution'

"Once Merseyrail get the work, they will subcontract it to private firms. This is a guinea pig for train operating companies to run their own infrastructure."

But Neil Scales, Merseytravel's chief executive, said: "The proposals for full local decision making on the Merseyrail electrics network are about investing in and continuing to improve the local rail network on Merseyside.

"We are seeking to provide local solutions to local issues by local people and we see this proposal as being a positive step forward for the people of and public transport on Merseyside."