Staff at EDF Energy in Exeter are among nearly 500 workers who have gone on strike again in an ongoing pay dispute.
The employees in the London, South Eastern, South West and Eastern regions started their 24-hour strike just after midnight.
Unite union leaders said the action would lead to delays in fixing and installing meters for customers.
The workers going on strike also include revenue protection staff dealing with business owners and private customers who are allegedly fiddling and stealing electricity.
The strike went ahead after talks last week, under the auspices of the conciliation service Acas, between Unite and EDF Energy broke down.
Unite regional officer Onay Kasab said: "Today's strike is very solid and sends out a clear message to management that they need to get around the table for urgent and constructive talks, otherwise more industrial action will go-ahead.
"Workers are taking action because EDF is refusing to honour an agreement it freely signed and to make matters even worse the company is offering a pay deal for 2013 which does not even keep up with the ever rising cost of living.
"The strike today is even better supported than the two days in May which shows the depth of anger at the company's behavior."
The latest strike will be followed by selective industrial action and a work-to-rule which starts immediately afterwards.
From tomorrow, Unite is instructing members to take action short of strike action on a continuous basis. The dispute has already seen two days of strike action at the beginning of May.
The workers have rejected a 2013 pay offer of two per cent and a non-consolidated, one off payment of £200 for the year April 2013 to April 2014.
Other aspects of the dispute are specific to workers in the South East and Eastern regions.
The EDF centres affected by the industrial action are at: Osprey House in Sowton and Gadeon House on Exeter Business Park; Bexleyheath in Kent; London; Crawley; Bristol; and Plymouth.
A spokesman for EDF Energy said: "We have offered employees working in our metering division a final pay offer of two per cent with an additional lump sum of £200.
"The negotiations relate to the 2013 pay deal, which once agreed would be backdated to last April.
"We believe our final offer is fair and competitive."
