Around 50 Unite union members at the Stonebyres, Cruachan and Glenlee hydro-electric power stations have voted to strike by 84.6%, on an 86.7% turnout.
The Drax Hydro workers also voted by 92.3% to take action short of a strike, which would involve an overtime ban.
They include engineers, plant controllers, as well as mechanical and electrical craft workers.
