The RMT - which represents many drivers and station staff - says it called for industrial action because London Underground refused to discuss what would happen to employees if the system is privatised.

The union wants assurances that there would be no compulsory redundancies if private companies take over.

Members of the RMT voted by 2,471 (84.2%) to 462 (15.8%) to take action.

The union's executive will decide on Thursday whether to name dates for strikes or other forms of industrial action that would disrupt Tube services.

Services face disruption

Assistant general secretary Bob Crow said: "The vote shows the overwhelming concern felt by London Underground employees for their jobs and conditions of employment."

He warned that industrial action by RMT members, including train drivers and station staff, would seriously disrupt services.

The executive will consult local union officials before deciding on the form of industrial action, but Mr Crow made it clear there will be strikes unless there are peace moves in the next few days.

"Strikes will have a massive impact on services," he warned.

The turnout in Wednesday's ballot was 49% but the union said the outcome showed the level of concern among workers for their jobs and conditions of employment.

'Great future'

Mr Crow said the union had been trying for months to meet with London Underground to discuss the effects of privatisation.

London Underground said there was nothing to be gained from taking strike action and maintained that the Tube faced a "great future".

A spokesman said: "We have just secured excellent funding from the government and a deal that holds out the prospect of long-term security.

"The last thing we need now is a strike - it just does not make sense."