More strike action could be looming on the railways after a government decision to take signalling work out of the hands of Network Rail.
Transport secretary Alistair Darling said responsibility for signals would pass to Mersey Rail under a pilot scheme.
However, the RMT union said the scheme to shift 67 signalling workers to Mersey Rail was the "thin end of the wedge" to handing responsibility for signalling operations and maintenance back to the private sector.
RMT general secretary, Bob Crow, said signalling operations and rail maintenance under the control of Network rail had been one of the industry's recent success stories, and transferring responsibility to private operators could reverse those achievements.
"We cannot rule out industrial action to prevent our members' terms and conditions which could be threatened by this transfer," he said.