GMB union officials waved placards, handed out leaflets, and dressed as robots to highlight the 'plight' of workers at the online retailer's Rugeley depot yesterday.
Union bosses said Amazon staff were 'treated like slaves and robots' who were reprimanded for taking toilet breaks – a claim the firm categorically denies.
GMB West Midlands regional organiser Rebecca Mitchell said: "Every other week we are hearing of complaints about the working environment and conditions at Amazon.
"We are here to provide a voice for our members. Companies like Amazon should treat staff with respect instead of treating them like slaves and robots.
"Our members have been quizzed over taking toilet breaks – leaving them scared to go to the toilet when on shift.
"They are also threatened with disciplinary action if they fail to achieve a 100 per cent 'hit rate' in their productivity when picking or packing.
"Our members are hard working people who simply want to be able to put food on the table and clothes on their children's backs, they deserve to be treated like humans."
The small gathering of union officials and representatives met from 6am to 7am during a shift change at the 700,000 square foot site, which opened in 2011.
Some of those making their way into the site stopped and picked up leaflets and union membership forms from the protesters.
Express & Star Comment: Questions remain at Amazon
Others declined attempts to hand them union literature.
The GMB does not have official union recognition at the site but said it represented a 'large percentage' of workers.
Up to 4,000 people work at the former Lea Hall Colliery site, with around 1,500 permanent employees.
Speaking on condition of anonymity, an instructor who teaches pickers how to do their job, said: "It's hellish. It's no fun. It's not a question of the volume of work but the pressure you are put under. You go to the toilet and get questioned over what you were doing and why you were so long. It's slave labour."
Amazon said it allows staff toilet breaks and that employees can go to the toilet whenever they need to.
A source, who works at the site, dismissed claims that morale was low at the site.
They told the Express & Star that yesterday – the same day as the protest – workers were treated to a Christmas meal.
Amazon is Rugeley's biggest employer and one of the biggest firms in Staffordshire.
The company, which has faced criticism over its working conditions in recent years, previously said: "Amazon provides a safe and positive workplace with competitive pay and benefits from day one. We are proud to have created thousands of permanent roles in our UK fulfilment centres in recent years.
“We offer great jobs and a positive environment with opportunities for growth. As with most companies, we expect a certain level of performance.
“Targets are based on previous performance achieved by our workers. Associates are evaluated over a long period of time as we know a variety of things could impact the ability to meet expectations in any given day or hour.”