Hundreds of workers at energy giant EDF are to stage a 24-hour strike in a row over pay.
Unite said almost 500 of its members, including meter readers, based in London, southern and western England, will walk out on September 2 following the breakdown of talks.
The union said the action could hit the roll out of a smart meter installation programme.
Unite official Onay Kasab said: “We entered talks hopeful that we could avoid industrial action and are deeply disappointed by the company’s refusal to give concrete assurances on protecting current pay, conditions and hours.
“Our members cannot stand by and let previous agreements be torn up and their pay, terms and conditions eroded.
“Some members of staff face a £6,000-a-year drop in income while others face losing their job.”