Working at an Amazon warehouse in the U.K., James Bloodworth came across a bottle of straw-colored liquid on a shelf. It looked like pee.

How could he be sure? "I smelt it," said the 35-year-old British journalist and author, talking about his new book "Hired: Six Months Undercover in Low-Wage Britain." It was definitely pee, he said.

As he tells it, urinating into a bottle is the kind of desperation Amazon forces its warehouse workers into as they try to avoid accusations of "idling" and failing to meet impossibly high productivity targets — ones they are continually measured against by Big Brother-ish type surveillance.

It didn't help that the nearest bathroom to where he worked was four flights of stairs below.

Bloodworth's grim picture of Amazon's blue-collar workplaces — he compares the warehouse he worked in, alternately, to a prison and a totalitarian state — is bringing new attention to the company's treatment of its workers. Out in the U.K. since March, and just appearing in this country, "Hired" sparked a flurry of reviews in the British press and some American coverage as well.

Adding to concerns that have festered for years, Bloodworth's depiction arises as the company rapidly expands its warehouse operation, where workers store, pack and ship the items customers order online. Amazon last year said it employed 125,000 full-time workers in the U.S., 38 percent more than a year ago.

The company has not released worldwide employment figures, but said it has 175 "fulfillment centers," as it calls its massive warehouses where goods come in and out, and 35 smaller "sortation centers" that finish off the delivery process.

"We don't recognize these allegations as an accurate portrayal of activities in our buildings," the company said in a statement about Bloodworth's book. The statement touted Amazon's above-minimum-wage warehouse pay ($11 after two years in the U.K. and an average $15 in the U.S.) and benefits.

There were, however, echoes of Bloodworth's book even on a warehouse tour in Kent with an Amazon PR manager looking on.

"We are allowed to go [to the bathroom]," said one worker, "but you can't stay for that long." Four or five minutes is OK — "six minutes tops."

Anyway, he said, if you spend too long, "the numbers start to bite you," meaning the rate of tasks per hour by which workers are measured, will drop unacceptably.

Sheheryar Kaoosji, co-executive director of the Warehouse Worker Resource Center, a nonprofit in Southern California that advocates for better working conditions, said all warehouse employers try to get workers to do their jobs as quickly as possible. But because of the way Amazon uses technology, he said, "it's definitely a whole other level."

Bloodworth said he spent several weeks at Amazon in early 2016 working the requisite 10-hour shifts, four days a week, at a warehouse in the West Midlands countryside. Seeking to write about the plight of the working class, he also worked at a call center, as an Uber driver, on a building site and as a home aide caring for the elderly.

"Amazon was the worst employer, easily," the author said by phone.