While consumers participate enthusiastically in Prime Day, a sales bonanza staged each year by Amazon, the company’s workers regard it with something less than enthusiasm.

The $5 billion in sales the world’s biggest online retailer is predicted to generate over the 2-day event is expected to exacerbate what are alleged to be already stressful conditions for the company’s employees.

The sale comes amid criticisms about safety and health hazards in Amazon warehouses that largely stem from production pressure. The company has been named several times to the “Dirty Dozen” list of unsafe employers compiled by the National Council for Occupational Safety and Health (National COSH). Amazon’s recent acceleration to a one-day shipping policy is expected to intensify the speed at which Amazon workers are under to perform their tasks – selecting, sorting and shipping items – at high speeds.

Workers at an Amazon Fulfillment center in Shakopee, Minnesota staged a six-hour strike yesterday to protest their working conditions.

The company released a statement in response that it already offers what the workers were demanding.

More than a half a million people work at 140 Amazon fulfillment centers in the U.S. The company reportedly gives workers a special Prime Day t-shirt and a snack as a bonus.

“Amazon has a well-documented history of mistreating and dehumanizing its workers in the U.S. and around the world,” Stuart Appelbaum, president of the Retail, Wholesale and Department Store Union, said in a statement. “The stress can be particularly hard on any day, and especially during Prime Day events. But, this year, the toll on Amazon’s workers will be considerably worse.”

“Amazon needs to understand that human beings are not robots,” Appelbaum said.