Amazon (AMZN - Get Report) Prime Day kicked off on Monday, but not everyone is thrilled about the latest discounts and offers from the e-commerce giant. 

Amazon workers in four geographies are holding strikes for Prime Day, which runs Monday through Tuesday, and calling attention to the working conditions at Amazon fulfillment centers. Amazon employs about 647,500 workers worldwide and about 300,000 in the U.S., and the worker strikes are taking place in Minnesota, Germany, Spain and Poland.

It's not the first time Amazon workers have spoken up about low pay and poor conditions at fulfillment centers -- but Amazon's plans offer one-day shipping to Prime members make the message all the more salient, according to Stuart Appelbaum, President of the Retail, Wholesale and Department Store Union (RWDSU).

"Amazon fulfillment workers were already facing speeds of 200-300 orders per hour in 12-hour shifts before the new policy. They were struggling to maintain that pace, even before the one-day shipping policy was announced. Testing hundreds of thousands of workers physical limits as though they were trained triathletes is the wrong approach," Appelbaum said in a statement.

The Prime Day strikes also come soon after a recent announcement by Amazon that it will spend $700 million to retrain one-third of its workforce by 2025 to move them onto more advanced career tracks. In addition to thousands of human workers, Amazon operates a growing range of robotics and automated systems in its fulfillment centers.

Marc Perrone, President of the United Food and Commercial Workers International Union, dismissed the retraining plan as too little, too late.

"Amazon is throwing money at a problem it created and somehow thinks that it deserves applause. This is an insult to the thousands of Amazon workers who are forced to endure dangerous working conditions and meet impossible demands every day," Perrone said. "Amazon has become an economic arsonist that suddenly decided to put out the fires it is starting."

In a statement to TheStreet, an Amazon spokesperson dismissed the strike participants as misinformed. 

"Events like Prime Day have become an opportunity for our critics, including unions, to raise awareness for their cause, in this case, increased membership dues. These groups are conjuring misinformation to work in their favor, when in fact we already offer the things they purport to be their cause -- industry-leading pay of $15 per hour, benefits and a safe workplace for our employees. We can only conclude that the people who plan to attend the event on Monday are simply not informed," the spokesperson wrote. 

Amazon shares rose 0.5% to 2,020.99 on Monday and are up 30% so far this year. The company's market cap is within $5 billion of $1 trillion. 

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