One of the UK's biggest unions, GMB, will stage a protest at an Amazon event in Manchester on Monday over warehouse worker conditions.

GMB wants to draw wider attention to allegations by current and former workers about strict productivity targets, health issues, and that people are too scared to go to the bathroom.

Amazon has successfully battled unions in the US.

The company has pushed back on allegations of poor worker treatment and said it doesn't recognise media portrayals of its warehouse conditions.

One of the UK's biggest trade unions will protest outside an Amazon event in Manchester today over the way the retail giant treats its warehouse workers.

GMB organised its demonstration after Business Insider's coverage of author James Bloodworth's experiences working undercover at an Amazon fulfilment centre in Rugely, in central England.

Bloodworth told Business Insider of his experiences working as a "picker" collecting items in the warehouse, and said he had come across a bottle of urine on the shelves. He attributed this to workers being too scared to take a toilet break, for fear of being punished for time off the job.

GMB national staff member Mick Rix told Business Insider that the union had around 1,000 Amazon staffers as members. The demonstration will be comparatively small at around 30 or 40 people, but the idea is to call attention to the firm's treatment of staff.

"We have decided to rock up and make a little bit of noise," Rix told Business Insider ahead of the protest on Tuesday morning. "We want to bring attention to a number of things that Amazon are doing in terms of their treatment of workers, and its all-aggressive way of operating."

The event in question is designed to encourage third-party sellers to use Amazon Marketplace to sell their wares overseas, and is being held in Manchester today with the Department for International Trade.

In the US, Amazon has reportedly successfully fended off trade unions, and the picture is similar in the UK, according to Rix. Part of the reason is the high turnover rate of workers, many of whom are employed on a temporary basis, and the fact that union members are spread across Amazon's many warehouses in the UK.

"Trade unions make the workplace safer," argued Rix. "We bring enormous expertise into regulating working practices and the whole issue is not about fighting the company's productivity, it's about doing things in a smarter way."

Some of the measures Rix would like to see include more breaks introduced for warehouse workers. He would also like to see workers be able to "slow down" during the day. Amazon currently sets its workers strict targets to hit which, according to former employees speaking to Business Insider, can feel impossible to hit.

GMB's demonstration comes after a bigger protest in Berlin, involving around 450 people. German warehouse workers gathered outside the offices of publisher Axel Springer, where Amazon CEO Jeff Bezos arrived to collect an award and give an on-stage interview. Axel Springer is Business Insider's parent company.

At the time, Bezos addressed criticism about the way the company treats staff. He said critics were wrong about the company, and that he was proud of the way Amazon treated staff.

"On the issue of working conditions, I'm very proud of our working conditions and very proud of the wages we pay," he said. "You know, in Germany we employ 16,000 people, and we pay at the high end of the range for any comparable work."

Amazon has also pushed back on allegations from former workers that it treats staff badly.

"Amazon provides a safe and positive workplace for thousands of people across the UK with competitive pay and benefits from day one," the company told Business Insider last month. "We are committed to treating every one of our associates with dignity and respect. We don't recognize these allegations as an accurate portrayal of activities in our buildings."