Control room staff at the National Grid will start an overtime ban this week as a result of pay discrepancies.
National Grid has committed itself to harmonising its pay structure, but negotiations over remuneration have taken more than a year and employees at the firm are looking to get their pay rises backdated.
Prospect national secretary Emily Boase said: "It takes a lot to push control room staff, who are professional engineers dedicated to safe and continuous operation of the nation's power supply, to take industrial action."
The union is supporting 119 members of staff from National Grid's Electricity Operations Control Centre in Wokingham and Network Operations Centre at Warwick, in their mission to get backdated pay.
Some 93 per cent of Prospect members voted in favour of the overtime ban.
A spokesperson for the company said National Grid had already taken steps to ensure there was no disruption as a result of the action.
National Grid is one of the world's largest utilities firms with operations in the UK and US.
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