London Underground workers are to be balloted for industrial action in a row over pay, it was announced today.
The Rail Maritime and Transport union said its members working in the Tube's power control room will vote on whether to take action short of a strike.
General secretary Bob Crow said: "We have tried to negotiate a solution to our members' concerns over power room grade progression but the company have failed to come up with a serious package that meets past promises they have given us on pay parity and additional benefits at the top of the pay band.
"Our members rejected the latest proposals by 100% and we now have no option to move to a ballot for action involving these essential staff who power up the entire Tube system. We have no doubt they will deliver a rock solid mandate.
"We hope that a strong yes vote will force the company back to the negotiating table with a substantially improved offer."
Meanwhile, Mr Crow will meet London Mayor Boris Johnson on Friday for their first head-to-head debate since Mr Johnson was elected when they appear on BBC Radio 4's Any Questions programme.
Mr Crow said: "With the focus in the run-up to Saturday's big TUC demonstration all on this Government's cuts agenda there can be no better time for the Mayor of London to at last agree to have a proper discussion, in public, with a Tube union official."
A Transport for London spokesman said: "London Underground has been working with all unions on developing new ways for power control and track access control staff to progress in their careers.
"LU's proposals would see most staff given pay uplifts and would be based on the introduction of a new skills framework to give staff a clear guide on the performance required to progress. Discussions are ongoing and we would urge the RMT to continue with constructive talks."
* Commuters faced long delays getting into work today after services had to be suspended on a large section of a busy Tube line.
Due to a problem at Wembley in north west London, the Metropolitan line had no trains running between Harrow-on-the Hill and the City of London.
Early-morning trains banked up at Harrow, with hundreds of passengers having to end their London-bound journeys there.
They were forced to try to fight their way on to Chiltern main line trains travelling from Harrow to Marylebone station in London.
Transport for London (TfL) said later that the disruption had been caused by a derailment of an empty train in sidings at Wembley and no one had been injured.
A TfL spokeswoman said: "We apologise to passengers for the inconvenience this caused.
"The incident was caused by driver error, and our safety systems worked correctly in preventing the train from leaving the sidings. We stress that no passengers were involved or endangered during the incident."
After the initial crush of passengers at Harrow, services into London were quickly restored, although there were minor delays at the western end of the line between Chesham and Chalfont and Latimer.