Thousands of British Gas workers are being told to accept new working conditions, including no extra overtime pay, or risk their jobs.
The firm said if employees don’t sign new contracts, there will be a fresh wave of layoffs, although it insists this would be a “last resort”.
Centrica, which owns British Gas, has already outlined 5,000 job cuts as a knock on effect of the pandemic, with new customer numbers also falling in recent years.
The firm said it had “been open about the changes” needed to win back customers.
The proposals are all subject to a consultation period with unions, the company said.
“Our employees’ base pay and pensions will be protected, but simplifying and modernising their terms is essential if we’re to become more flexible and price competitive,” said Centrica.
“We have over 80 different employee contracts with 7,000 variations of terms, many of which are outdated and stop us delivering for customers.”
Centrica proposes to fix overtime pay at the same rate as regular hours, according to a presentation seen by the BBC.
Previously, overtime could attract double the hourly rate, depending on a worker’s contract.
Engineers who might previously have been asked to work shifts between 08:00 and 20:00 in the busier winter period could be allocated hours any time between 06:00 and 23:00.
Centrica said a so-called Section 188 notice, which employers are obliged to give to workers’ representatives if they are considering large-scale layoffs, was a last resort if workers did not agree the new terms.
“We’ve been open about the changes we need to make to win back customers, grow our company and protect jobs in the long run,” the company said in a statement.
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The company said it is hoping to reach a deal with employees before winter, with the GMB union now in talks with the firm.
Assistant general secretary Christina McAnea of the Unison union branded the move “disgraceful behaviour”.
“Employees have worked hard throughout the past few months to ensure customers are well-served, despite the pandemic,” she said. “This is no way for company directors to repay them.”
Last month, Centrica began trialling a cheaper, digital-only brand under the name British Gas X.
The Big Six energy company has revealed a new digital-only energy which could offer lower bills in competition with a rise in the number of low-cost rivals on the market.
Centrica has about 27,000 employees, with 20,000 of these based in the UK.