Workers at shipbuilder Cammell Laird could strike over concerns of up to 300 job losses despite recently being awarded huge Royal Navy contracts.
Earlier this month it was announced that the Birkenhead shipyard would receive £620m to support Royal Fleet Auxiliary tankers.
However, the Unite union said about 40% of jobs could go by March 2019, and now over 300 members have unanimously backed an industrial action ballot.
Cammell Laird said jobs were "at risk".
The threat of redundancies has caused a "real anger among the workforce", according to Unite regional officer Ross Quinn.
"They should be celebrating and looking forward to a secure future after winning a massive contract to maintain ships for the Royal Navy," he said.
"Instead workers feel totally sold down the river and fear being put out of a job to be replaced by agency labour at a later date."
He added that Unite members will use "use every tool at our disposal" to save shipbuilding jobs on the Mersey.
A Cammell Laird spokesman said he was unable to confirm the number of potential redundancies as the firm was still "bidding for new contracts to maintain staffing levels".
He added that with "numerous contracts entering the latter phases" and no certainty of similar deals "in the immediate term", the company must "address its cost base to remain competitive".