Amazon workers in Spain have walked out in a protest over working conditions and pay during one of the US retail firm's busiest sales events, Prime Day.

Thousands of Spanish workers were absent from fulfilment centres yesterday and today, with the strike set to continue until Wednesday.

Amazon also expects to see workers in Germany walk out later today while employees in Polish fulfilment centres are staging a work to rule protest.

The Seattle-based company kickstarted its Prime Day discounts at midday yesterday (7am EDT), with offers set to run until midnight tonight (7pm EDT), however fears are mounting the retailer will be unable to satisfy the surge in demand with a depleted workforce in its fulfilment centres.

Amazon's woes were compounded earlier today when it suffered technical issues with its online services due to the heavy web traffic from bargain-hunters, which left many customers unable to access the site.

Reports also flooded in from disgruntled customers who were left unable to access the company's online platforms, including Prime Video, and voice assistant, Alexa.

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Amazon workers in Spain have walked out in a protest over working conditions and pay during one of the US retail firm's busiest sales events, Prime Day. Thousands of Spanish workers were absent from fulfilment centres yesterday

Ana Berceruelo of the Spanish Worker's union (CCOO) claims up to 80 per cent of workers at the fulfilment centre in San Fernando de Henares, near Madrid, have walked out in protest.

Across Spain, the number of people striking is tipped to be close to 2,000.

The protest is expected to continue through until Wednesday.

Meanwhile, Verdi, a German trade union group based in Berlin, has called a one-day strike to coincide with Amazon's Prime Day sales event over demands for labour contracts that guarantee better working conditions inside the retail giant's fulfilment centres.

The workers say the job involves long periods of standing, walking long distances and repetitive tasks.

Verdi did not specify how many people it expected to participate in the strikes.

'The message is clear — while the online giant gets rich, it is saving money on the health of its workers,' said Stefanie Nutzenberger, the top Verdi official for the retail sector.

The one-day strike will take place at six facilities across Germany, and is set to coincide with a three-day strike planned in Spain.

Meanwhile, Polish workers are set to stage a work-to-rule protest – performing no more than the minimum requirements of their contract while following regulations to the letter, which in practice will results in delays for customers, Verdi said.

Amazon says it only expects a fraction of its 12,000 workers in Germany to join the strike, and that there should be no noticeable impact on Prime Day deliveries.

Fulfilment centre workers based in Britain do not have a designated trade union, however, GMB has previously staged demonstrations to protest working conditions in the UK warehouses.

This is not the first time Amazon employees have gone on strike this year.

Back in March, hundreds of workers walked out of the Seattle retail company's warehouses over a dispute around working contracts.

Timing the strike to occur during an important sales day for the retailer is a tactic previously used by disgruntled Amazon fulfilment centre workers.

In 2017, workers in Germany and Italy orchestrated a walk-out to coincide with Black Friday.

Complaints by fulfilment centre workers focus around long, gruelling shifts and inadequate financial compensation.

Across Spain, the number of people striking is tipped to be close to 2,000. The protest is expected to continue through until Wednesday

Amazon claims its fulfilment centre jobs offer competitive pay and comprehensive benefits from the first day of employment.

'We believe Amazon's Fulfilment Centre jobs are excellent jobs providing a great place to learn skills to start and further develop a career,' the company said.

Permanent staff earn £10.82 an hour ($14.31) and are due an increase in pay after two years in the job.

Amazon Spain said on Monday that it paid competitive wages for the logistics sector and that it planned a 2.5 per cent wage hike for recent hires and an increase of 5.6 per cent for those with at least four years of experience.

Amazon has said its fulfilment centre jobs offer competitive pay and comprehensive benefits from the first day of employment, however staff complaints focus on long, gruelling shifts and inadequate financial compensation

These claims of improved wages come only days after Amazon CEO Jeff Bezos became the first man in history to be worth $150 billion (£113.5 billion).

Bonnie Castillo, union activist and executive director of the National Nurses Union, said: 'The median Amazon employee earns $28,000 in a year.

'Jeff Bezos makes more than that in 10 seconds.

'If Bezos shared even half of his wealth with his 566,000 employees, they'd each get $231,449.'

The $150billion mark breaks the record once held by Microsoft founder Bill Gates, who at the height of the dot-com boom was worth $149billion after adjusting for inflation.

In 1999, Gates’ net worth hit its peak, reaching $100billion, which in today’s dollars translates into $149billion.

WHY HAS AMAZON BEEN CRITICIZED FOR ITS TREATMENT OF EMPLOYEES? Amazon has been accused of 'dehumanizing' its staff to deliver products to customers. Workers at the internet shopping giant's distribution centers face disciplinary action if they lose a punishing race against the clock to track down items ordered by online shoppers. Staff paint a picture of a stressful environment ruled by the bleeps of handheld devices – nicknamed 'the gun' – instructing them which items to collect. Bosses are said to push staff so far past breaking point that they 'practically combust', while regular sackings to keep workers on their toes were described by one HR manager as 'purposeful Darwinism'. According to an expose last year, the company's best workers are known as 'Amabots' – because they are so 'at one with the system' they are almost cyborgs. In November shocking claims were made about the online retailer’s newest warehouse – which the company refers to as a ‘fulfilment centre’ – in Tilbury, Essex. The packing plant is the biggest in Europe, the size of 11 football pitches, and is due to ship 1.2million items this year. In November shocking claims were made about the online retailer’s newest warehouse – which the company refers to as a ‘fulfilment centre’ – in Tilbury, Essex The investigation, by an undercover reporter for the Sunday Mirror who spent five weeks there, suggested workers suffer mentally and physically as they try to meet demand. He said that some of his colleagues were so tired from working 55-hour weeks that they would ‘sleep on their feet’. ‘Those who could not keep up with the punishing targets faced the sack – and some who buckled under the strain had to be attended by ambulance crews,’ he added. Just the following month it emerged Amazon delivery drivers are asked to drop off up to 200 packages a day, are paid less than minimum wage and urinate in bottles because there's no time to take a break Legal firm Leigh Day, which led a case against taxi giant Uber, is representing seven drivers who say the agencies used by Amazon are mistreating them. While Amazon does not employ the drivers directly, the drivers, who are recruited through agencies, work via an Amazon app and follow delivery routes made by the company. But drivers who are given up to 200 packages a day to deliver, say that traffic jams, weather and speed limits make it near impossible to deliver all of the parcels in a timely fashion. A spokesperson for Amazon said: 'Amazon provides a safe and positive workplace. The safety and well-being of our permanent and temporary associates is our number one priority.' Advertisement

For years, Gates and Bezos were neck-and-neck in the race to be the world’s richest human.

According to a poll of 100 Amazon workers, more than half said they suffered from depression, and eight people said they had thought about killing themselves.

James Bloodworth, who worked ten-hour shifts at a warehouse in Rugeley, Staffordshire, claimed staff resorted to urinating in bottles because they were so terrified of getting in trouble for taking toilet breaks.

The Rugeley warehouse measures 700,000 sq ft (65,000 sq metres), with some of the 1,200 workers faced with a ten minute, quarter-of-a-mile walk to the two toilets found on the ground floor of the four-storey building.

He said: 'For those of us who worked on the top floor, the closest toilets were down four flights of stairs.'

Mr Bloodworth, who worked as a picker selecting goods for dispatch, walked ten miles a day in the job while researching a book on low-wage Britain.

He revealed workers were continually monitored for time wasting by supervisors and claimed the strictness was what caused the 'toilet bottle' system.

Amazon has refuted these allegations.

In a statement to MailOnline, Amazon said: 'Amazon provides a safe and positive workplace for thousands of people across the UK with competitive pay and benefits from day one and we don’t recognise these allegations as an accurate portrayal of activities in our buildings.

'We have a focus on ensuring we provide a great environment for all our employees and earlier this year Amazon was named by LinkedIn as the 7th most sought after place to work in the UK and ranked first place in the US.

'Amazon also offers public tours of its fulfilment centres so customers can see first-hand what happens after they click “buy” on Amazon by visiting uk.amazonfctours.com.

'Amazon ensures all of its associates have easy access to toilet facilities which are just a short walk from where they are working. Associates are allowed to use the toilet whenever needed. We do not monitor toilet breaks.'