Construction and maintenance workers employed by Tube Lines on London Underground have voted to strike over jobs, pay and conditions.
The Rail Maritime and Transport Union said its members backed industrial action by a margin of nine to one, according to the Press Association.
Transport for London is buying out Tube Lines for £310m, effectively bringing the London Underground back under public sector control, along with its maintenance and upgrade programme.
However, RMT said there was still uncertainty over its members' jobs, conditions and pay.
No dates have been set for the strike action yet.