Metronet looked after the maintenance of nine Tube lines

Earlier this month Metronet, which is responsible for the upkeep of nine Tube lines, went into administration.

The company had projected an overspend of �2bn by 2010.

The RMT Union and Transport Salaried Staffs' Association (TSSA) said the firm has not given job and conditions guarantees for 2,600 workers.

Transport for London (TfL) has called the ballots "unreasonable" saying nobody has proposed actions that may affect the staff members.

'Last desperate throw'

Bob Crow, the RMT general secretary, said: "We warned from the start that we would not allow our members' jobs and conditions to be decimated by Metronet's death throes.

"It is unacceptable that our members face losing 10% of their pensions because Metronet's fat cat shareholders decided to pull the plug."

Manuel Cortes, TSSA assistant general secretary, said: "These job losses were the last desperate throw by Metronet to avoid administration. As we all know, this gamble failed."

A TfL spokesman said: "It is unreasonable to call strike ballots against actions which nobody including the administrator has proposed.

"Calling strike ballots at the drop of a hat is no way to address the difficult situation created by Metronet's failure."

The strike ballots will open on 7 August.