A union has held protests outside Amazon warehouses to coincide with the Black Friday sales.
GMB members gathered in Sheffield, Rugeley and Peterborough. Amazon said no workers had been involved in the protests.
The union said the protests came after "more than 600 ambulance call-outs" to Amazon warehouses in three years.
Amazon said "self-interested critics, particularly unions" had "a vested interest in spreading misinformation".
Amazon said the protests involved "a total of 30 external, pro-union people" at a small number of its 50 UK sites.
The action came as protesters in France and Germany also targeted the firm.
Mick Rix, GMB national officer, said they wanted Amazon founder Jeff Bezos, 55, "to know they are people - not robots".
"It's about time Mr Bezos showed empathy with the very people that have helped build his vast empire and make sure it is not a Black Friday for Amazon workers."
GMB said its members had described Amazon's targets as "so horrific" they had to use plastic bottles to urinate in instead of going to the toilet, with pregnant women forced to stand for hours on end.
It claimed at least one woman had reported losing a pregnancy at work, but no ambulance was called and she had to go home on the bus with her co-workers in blood-stained clothes
Earlier this year, Amazon started offering public tours of its warehouses so members could "come and see for yourself" what conditions were like.
An Amazon spokesperson said: "Self-interested critics, particularly unions, have a vested interest in spreading misinformation about Amazon but the facts tell a different story.
"The truth is that Amazon already offers industry-leading pay, starting at £9.50 an hour, comprehensive benefits, as well as a safe, modern work environment.
"These groups are conjuring misinformation to work in their favour, when in fact we already offer the things they claim to be fighting for.
"You don't have to take our word for it - or theirs. Come and see for yourself by registering for a tour at one of our fulfilment centres."
GMB protesters are planning further action outside Amazon's London headquarters on 2 December to coincide with Cyber Monday.