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Employee working conditions are reportedly so demanding at Amazon that some delivery drivers are forced to pee in bottles.

The working conditions and physical demands of the job don't leave much time for bathroom breaks or rest periods, according to driver complaints.

Amazon CEO Dave Clark welcomed Sen. Bernie Sanders' upcoming visit to an Amazon fulfillment center in Bessemer, Alabama on Friday, March 26, where employees will vote on whether to form a union.

"...if you want to hear about $15 an hour and health care, Senator Sanders will be speaking downtown. But if you would like to make at least $15 an hour and have good health care, Amazon is hiring," Clark tweeted.

But Rep. Mark Pocan, a Democratic congressman from Wisconsin, criticized Clark.

"Paying workers $15 [an] hour doesn't make you a 'progressive workplace' when you union-bust [and] make workers urinate in water bottles," Pocan said on Wednesday night.

Clark hopped into the comments on Twitter and denied "the peeing in bottles thing."

"You don't really believe the peeing in bottles thing, do you? If that were true, nobody would work for us."

But an Amazon driver responded in the comments by posting a photo of urine-filled bottles.

"We're pressured to get these routes done before night time and having to find a restroom would mean driving an extra 10 minutes off path to find one," an Amazon delivery driver told Motherboard. "Ten to fifteen minutes to find a bathroom can add up, meaning 20 to 30 minutes there and back all together."

Another Amazon driver in Florida confirmed:

"All the guys do it... The best drivers get overtime so there's incentive to cut corners. The most productive drivers get rewarded the most hours."

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