On the biggest shopping day of the year, U.K.-based trade union GMB is organizing a protest against Amazon for what it calls "inhuman" conditions for warehouse workers.

Amazon has been under a microscope recently as it gets ready to bring 25,000 jobs to each of two new "headquarters" locations in New York and Arlington, Virginia. Since the announcement earlier this month, politicians and residents in those areas have questioned the benefit Amazon will bring to their cities as the influx of new workers will likely cause a strain on infrastructure and spike housing prices.

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GMB bases its allegations in part on a report that ambulances had been called to Amazon warehouses 600 times over the past three years as of May, a Freedom of Information request filed by the union revealed. Of the calls, 115 were to a single facility in Rugeley with 1,800 to 2,000 workers, the Guardian reported. That compares to eight ambulance calls to a nearby Tesco facility of a similar physical size with about 1,300 workers, according to the Guardian.

In a statement, Amazon said, "Our European Fulfillment Network is fully operational and we continue to focus on delivering for our customers. Any reports to the contrary are simply wrong."

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In a separate statement, Amazon noted that it has created 25,000 well-paying jobs in the U.K. and addressed the allegations of unsafe working conditions.

"All of our sites are safe places to work and reports to the contrary are simply wrong," Amazon said. "According to the U.K. Government's Health and Safety Executive, Amazon has over 40% fewer injuries on average than other transportation and warehousing companies in the U.K. We encourage everyone to compare our pay, benefits and working conditions to others and come see for yourself on one of the public tours we offer every day at our centers across the UK uk.amazonfctours.com."

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GMB said in a press release that it expects hundreds to participate in the protests at five Amazon warehouses in the U.K. and that workers in Italy and Spain will also "take action." CNBC could not independently confirm how many people attended the protests.

"The conditions our members at Amazon are working under are frankly inhuman," GMB General Secretary Tim Roache said in the press release. "They are breaking bones, being knocked unconscious and being taken away in ambulances. We're standing up and saying enough is enough, these are people making Amazon its money. People with kids, homes, bills to pay — they're not robots."

GMB did not immediately respond to CNBC's request for comment.



-CNBC's Deirdre Bosa and Elizabeth Schulze contributed to this report.

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