Britain's largest union said on Tuesday it would hold a ballot for industrial action later this month over the closure of two coal-fired generation units at Drax Group's Selby power plant in north Yorkshire.
Unite said the ballot will include the option for strike action later in the summer.
Drax Group is planning to close two coal-fired units next April. The other four units are biomass, using wood chip pellets.
The coal-powered units will be potentially replaced by gas generation units, after a judicial review last month.
Unite said that when a pay deal was struck last year, it was agreed that there would be no compulsory redundancies amongst the 600-strong workforce, but the company has now backtracked on the agreement.
Drax said it has been talking to employees and unions for more than two years about the coal unit closures.
"We gave our employees over a year's notice - the job losses will take place in April 2021. This means we have time to support those affected to get the best outcomes for them," a spokeswoman said.
Unite said its members voted by 85% to proceed to an industrial action ballot later this month which could give the green light for strike action towards the end of July.
"The management has a window of opportunity to negotiate with Unite for a natural wastage scheme as workers leave the plant's employment," Unite's regional officer Shane Sweeting said in a statement.
(Reporting by Nina Chestney; editing by David Evans)