Thousands of workers in Amazon sites around the world are staging protests about pay and conditions as the online retailer begins its annual sale.
On Monday, Amazon starts offering discounts to its Prime service members.
Unions say that 2,000 workers are on strike in Germany, while in the US, workers in a Minnesota centre reportedly plan a six-hour stoppage. In the UK, week-long protests are planned.
Amazon says it offers great employment opportunities.
William Stolz, a picker at a warehouse in the Shakopee warehouse in Minnesota, told the BBC that workers wanted "safe, reliable jobs" from Amazon.
He says he has to pick an item about every eight seconds, or 332 per hour, for a 10 hour day.
"The speeds that we have to work are very physically and mentally exhausting, in some cases leading to injuries," he said.
"Basically we just want them to treat us with respect as human beings and not treat us like machines," he said.
Prime Day begins on Monday, but actually lasts 48 hours. The Seattle-based retailer, founded by Jeff Bezos, says new deals will launch as often as every five minutes "giving shoppers plenty of reasons to come back again and again".
One of the most valuable public companies in the world - making Mr Bezos the world's richest man - Amazon rang up total sales of $235bn (£188bn) of online sales last year.
In Germany, where Amazon employs 20,000 people, labour union Verdi said more than 2,000 workers at seven sites had gone on strike under the logo "no more discount on our incomes".
"While Amazon fuels bargain hunting on Prime Day with hefty discounts, employees are being deprived of a living wage," said Orhan Akman, retail specialist at Verdi.
In the UK, GMB union officials handed leaflets to workers arriving at the site in Peterborough in the East Midlands, and in the coming days protests are expected at other sites such as Swansea and Rugeley, in the West Midlands.
Mick Rix, GMB national officer, said: "Amazon workers want Jeff Bezos to know they are people not robots. It's prime time for Amazon to get round the table with GMB and discuss ways to make the workplaces safer and to give their workers and independence voice".
While the GMB was not calling on shoppers to boycott Amazon, he said customers could act.
"We're not calling for economic damage for Amazon," he said. "What we're asking for is for people to be aware. Leave feed back on Amazon".
In response, Amazon said it "provided great employment opportunities with excellent pay".
It encouraged people to compare its operations in Shakopee with other employees in the area.
In the UK, where it employs 29,500 people, a spokesperson said the company offered industry-leading pay starting at £9.50 per hour and was the "employer of choice for thousands of people across the UK".
It said its German operations offered wages "at the upper end of what is paid in comparable jobs" and it was "seeing very limited participation [in strikes] across Germany with zero operational impact and therefore no impact on customer deliveries".
In total, Amazon has a global workforce of 630,000, with 300,000 in the US.