Amazon workers in Britain are set to stage a fresh wave of strikes next month as a dispute over pay threatened to escalate, the country's third-largest union said Friday.

More than 500 workers at a warehouse in Coventry about 90 miles north of London will join a pair of three-day stoppages on April 16-18 and April 21-23, according to the GMB union.

News of the stoppages came as the union announced strike ballots were underway at five other Amazon sites across the Midlands.

GMB is testing the waters for stoppages among staff with indicative votes at Amazon facilities in Rugby, Coalville, Kegworth, Mansfield and Rugeley.

The union is seeking a raise to $18.50 an hour, up from the current $12.90 rate, to bring pay in line with Amazon employees in the United States, and improved working conditions.

Amazon announced a pay increase earlier this month but the union said the offer meant an average increase of between 1.8% and 2.5% and pledged to fight on.

"Amazon bosses have refused to talk to us about pay," GMB official Stuart Richards said in a Twitter post. "While the company made huge profits, they thought workers would give up if they offered them scraps. They got it very, very wrong."

Amazon has countered that less than 1% of its British workforce is involved in the Coventry dispute, while pointing to its recent efforts to increase pay.

"We regularly review our pay to ensure we offer competitive wages and we're pleased to be announcing another increase for our U.K. teams," an Amazon spokesperson said. "Over the past seven months, our minimum starting pay has risen by 10%, and by more than 37% since 2018. We also work hard to provide great benefits, a positive work environment and excellent career opportunities."

About 300 workers at the plant first walked off the job on Jan. 25, the first time the U.S. online retail giant has been hit by industrial action in the country.

Last year, workers at an Amazon warehouse in New York voted to establish the first-ever labor union in the company's history.

The GMB, however, is not recognized by Amazon and therefore is currently unable to negotiate with the company on behalf of its members, but union leaders told the BBC they are nearing enough members to force recognition from the company.

According to the GMB, Amazon U.K. reported that it paid just $13.3 million in tax in 2021, despite recording a pre-tax profit of $251.3 million

It added that pay for Amazon's British warehouse workers has increased 29% since 2018, and pointed to a $616 one-time payment it had made to help employees with the cost-of-living crisis.

The Amazon strikes come amid a winter of industrial discontent in Britain not seen since the late 1970s with wave after wave of strikes in sectors ranging from the railways and the postal service to health care and the civil service.

Earlier this month Amazon increased to 27,000 the number of jobs it planned to cut from its global workforce this year up from the 18,000 it announced in January, with CEO Andy Jassy citing uncertain economic conditions and a wave of rapid hirings in the past.

In an open letter to employees, Jassy said that the jobs would be eliminated over the next few weeks, mostly in advertising, its gaming service Twitch, cloud computing unit AWS and part of its human resources division.

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