MG Rover has been warned its survival is at stake after workers rejected a company pay and conditions offer made during the Christmas period.
They threw out an offer which included a 2.5% pay rise combined with an overhaul of flexible working arrangements, by a 2,275 to 1,127 vote.
There could now be a ballot on strike action.
Speaking on BBC Radio West Midlands Tony Woodley, national organiser of the Transport and Workers Union, said: “A strike is the last thing anyone can afford. This company cannot and would not survive a dispute. People feel they are not valued and that is extremely dangerous.
“That fact that MG Rover is surviving and selling vehicles in a very competitive market is in itself a tremendous achievement. But this is not a company that is out of the woods yet.”
MG Rover said it will continue negotiations with the T&GWU.