Amazon won praise when it raised its minimum wage to $15 an hour in October 2018. Since then, the company has responded to criticism over its working conditions by claiming it is an industry leader in compensation, but a Guardian investigation has revealed many workers take issue with this messaging, as serious workplace issues remain that they say are still not being addressed.

They include claims workers are being punished for injuries; the elimination of bonuses and stock options, which has lessened the impact of the wage rise; poor working conditions; higher productivity demands and the hiring of temporary workers who do not have the same benefits as Amazon staff.

Jade Velez says she is one such example. She started working as a packer at an Amazon fulfillment center in Robbinsville, New Jersey, in April. On 1 July 2019, Velez was working one of her four weekly 10-hour night shifts when she injured her shoulder.

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“I had many heavy items that entire work shift,” Velez told the Guardian. She left early due to the injury, getting home at 3am. “The pain was unbearable.”

Velez’s pain worsened and her arm became swollen. She showed up to her next shift and requested to be sent to AmCare, Amazon’s on-site first aid clinic, where she was given ibuprofen and ice and then told to return to work.

After trying to pack, Velez requested to be sent back to AmCare, where she was sent home. She used her unpaid time off for the remaining hours of her shift. The next day, Velez was called in for a mandatory overtime shift. She returned to AmCare and was finally referred to Amazon’s workers compensation claims insurer, Sedgwick, where she filed a claim.

On 8 July, Velez was informed her claim was denied without explanation.

“I have sustained an injury on their time, at their facility, during their work and now I’m being faulted for it as I am only liable,” said Velez. “To date, I have yet to see a doctor, since I was awaiting direction from Sedgwick and am still in pain and unable to fully utilize the weight of my shoulder area.”

She recently retained a lawyer to continue pursuing her claim.

An Amazon spokesperson told the Guardian in an email: “It’s more complicated than that and we’re not able to provide private medical information.” They added that their action had been in accordance with New Jersey state workers’ compensation laws.

Other workers have complaints about different aspects of Amazon’s working conditions.

“Amazon is leaning heavily on this compensation angle for a lot of their messaging, but they’re not addressing the core workplace issues workers are bringing up,” said William Stolz, a picker for two years at the Shakopee, Minnesota, Amazon fulfillment center who last month helped organize an employee walkout.

Stolz noted the Amazon minimum wage increase came with the elimination of monthly bonuses and stock options for employees. He also claimed that since the beginning of this year, his fulfillment center had exclusively hired temporary workers who don’t have the same job security and benefits as direct hires.

An Amazon spokesperson said 150 out of 1,500 workers at the Shakopee fulfillment center were currently temporary employees, and 100 temporary workers at the center had been hired into full-time roles this year.

“Most people who try to work here can’t keep up with the productivity rates and wash out,” said Tyler Hamilton, another Shakopee Amazon worker, who has to work a second job when Amazon doesn’t offer or mandate overtime shifts.

Devon Fischer, a picker at an Amazon fulfillment center in San Marcos, Texas, quit a few weeks ago after two years of employment due to rising productivity demands.

“Hitting rate got harder and harder to hit so I gave up and quit,” he said. “My body would hurt 24/7 and I couldn’t take it anymore. The last three months, a computer would decide whether to give me a write up or not. A computer shouldn’t get to do that.”

Amazon claimed productivity demands had increased only once over the past two years at this site.

In Charlotte, North Carolina, Kelsi Gast has worked for about two years at an Amazon fulfillment center that does not have air conditioning.

“The only type of air circulation we have in the building are the huge industrial fans that are on the ceiling and smaller, portable ones designated for each department. It doesn’t do much, though,” Gast said.

Another worker at a different fulfillment center in the Charlotte area, Wendy Jackson, said Amazon had ignored complaints from her and other workers about lack of air circulation and air conditioning.

“We’ve all complained we need more fans,” Jackson said. “One day I almost had heat stroke. I’ve tried telling them they need to do something. They keep saying they don’t have enough money to get more fans throughout the warehouse.”

Amazon denied the air conditioning allegations at Charlotte area warehouses.

In the Raleigh-Durham area of North Carolina, Jamie Sohn started working at an Amazon sorting center when it first opened in August 2018.

“At the beginning it was an incredible place to work,” said Sohn.

She said pallets of water were provided to workers as daily temperatures were in the 90s, but a few weeks into work, the water pallets were taken away, as a refrigerator for workers to bring their own water was to be provided but had yet to be installed.

“I was lifting, moving, and the next thing I know, I see one of the managers and I just threw myself at her because I was going to collapse. I was shaking and sweating. There was no water, no way of cooling down,” added Sohn.

An ambulance was called and she was brought to the hospital, but Sohn claimed Amazon’s workers’ compensation insurer, Sedgwick, denied her claim and refused to compensate her for the ambulance and emergency bills accrued from the incident.

She continued working at the sorting center until she was terminated in January 2019, after a box fell on her head, just weeks after she informed management the way the boxes were stacked posed a safety issue. Sohn was awarded an undisclosed settlement by Amazon for the second incident.

An Amazon spokesperson told the Guardian in an email: “We did settle with Ms Sohn but we still feel strongly that all appropriate steps were taken in accordance with state workers’ compensation laws and that we made every effort to ensure she was given accommodations and treatment for a healthy return to work.”

The spokesperson added: “Simply put, people would not want to work for Amazon if our working conditions truly were as our critics portray them to be during this period of record low unemployment and plentiful job opportunities. But 250,000 people choose to work for Amazon in our fulfillment network.”