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A manager for an Amazon warehouse came back from a stint of military duty, where he took part in a mission to help Americans affected by a natural disaster. But instead of a hero's welcome for his service, his boss greeted him with a snide comment that he had abandoned his Amazon post again.

That incident, which occurred a few years ago, was one of several times the manager said he was pressured by his boss to either scale back his military commitments or leave the military altogether so he could focus on his Amazon career. He's since left the company, after the same boss pressured one of his family members, too.

This man, a combat veteran with multiple overseas deployments, is one of three Amazon warehouse managers who told CNET they've faced pressure from their superiors to quit the military, with their bosses expressing concern about their time away for training and deployments.

The situations may violate federal workplace discrimination laws put in place to protect military service members with civilian jobs.

These incidents sharply contradict Amazon's prominent promotion of its military recruiting, including hiring veterans and those in reserve and part-time roles, with the company often saying it values service members' experience and proactive thinking.

It is against the law for civilian employers to pressure their Guard or Reserve workers to get out of the military. Joe Davis, Veterans of Foreign Wars

The assertions also come amid intensifying attention on Amazon's alleged mistreatment of its warehouse workers in the US, with unions and advocacy groups arguing that employees are overworked, closely monitored for even restroom breaks and forced to move ever faster to meet Amazon's delivery times. During the Prime Day sale this year, several protests took place, including one organized by Amazon workers at a Minnesota warehouse, to highlight these concerns.

The treatment of these three employees could fuel further scrutiny.

"During this whole conversation the implication was that I would have to at some point choose between the military and Amazon," the manager wrote a few years ago after a conversation with his boss. "And that to move up with Amazon and be successful I would have to put the military aside because he's yet to see anyone balance both."

Another warehouse manager in another part of the country said he's faced pressure, within the past year, over the time he's taken off for reserve military duty. He said he was told by his boss that he'd need to pick either Amazon or military service, with his boss saying he couldn't do both.

Following two conversations about this issue, his boss didn't bring up the topic again and the manager continues to work for Amazon.

"It shouldn't be this way," he said, adding that he's known about six reserve and part-time military employees who've left Amazon over the pressure to focus on the company.

A third manager in yet another part of the country said his boss became critical of his work performance immediately after he said he needed to leave for a weeks-long overseas military training exercise. When he got back from the reserve duty, he said, his boss quickly confronted him with a written report of performance issues he said were false. He started looking for a new job and left Amazon soon after.

"I had never been told my work performance was less than stellar," said the man, a combat veteran who worked for Amazon a few years ago. "There were no issues, none, until I notified them" about the training exercise.

All three warehouse managers requested anonymity for fear of retaliation from the company. Some details about them were left out to protect their identities.

Kerem Yucel/Getty Images

Amazon spokeswoman Rachael Lighty said the company is concerned about such allegations, asking employees to speak up about their needs.

"At Amazon, we are proud to employ and support more than 18,500 veterans, members of the Guard and Reserve, and military spouses across our businesses," Lighty said in an emailed statement. "We encourage all employees -- no matter their tenure, job title, level or background -- to bring their comments, questions, ideas, and concerns directly to their management team with the goal of improving the work environment and challenging leadership assumptions.

"We take this allegation seriously as this is not the culture we aspire to create for any of our employees," Lighty continued. "We remain committed to supporting our military and veteran employees and providing opportunities for their long-term career growth and success."

Under the federal Uniformed Services Employment and Reemployment Rights Act (USERRA), military veterans, reserve and part-time service members are protected from civilian workplace discrimination, including denying people promotions due to their military commitments, or the refusal to hire them outright. Army National Guard and Army Reserve soldiers, for example, spend a weekend a month plus two weeks a year in training. Guard deployments for duty can vary from as little as 15 days to as much as a year.

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Joe Davis, director of public affairs at the nonprofit service group Veterans of Foreign Wars, argued that these incidents at Amazon are USERRA violations.

"It is against the law for civilian employers to pressure their Guard or Reserve workers to get out of the military and to create a work atmosphere that is not conducive to future civilian employment and simultaneous military employment," he said.

Balancing military and Amazon

The Amazon warehouse manager who served during the natural disaster said his time at Amazon was difficult. The warehouse was usually hot, due to insufficient air conditioning, and he routinely lacked enough staff to complete needed tasks, he said. When mistakes occurred, he said, he'd usually get chewed out by one of his bosses.

"I didn't get treated as bad in the [military] in basic training," he said. "You screw up -- it's a screaming, cussing, yelling tirade on the floor."

Despite the high-pressure atmosphere, he said he stayed in his position as long as he did because of the generous pay, which was a big bump up from his prior job at a different company.

In addition to dealing with workplace problems, the manager said he was repeatedly pressured by his boss over several months to leave the military so he could spend more time at Amazon. This boss directly told the manager during one conversation that he'd eventually need to pick Amazon or the military, the manager said. The manager reported the conversation to a human resources employee at that warehouse but said the complaint went nowhere.

When the boss failed to convince the manager to leave the military, the boss approached a family member, telling that person the manager wouldn't be able to advance at the company if he continued to serve both the military and Amazon. In an interview with CNET, the family member confirmed the details of this conversation.

The manager said he'd eventually had enough and left Amazon a few years ago.

CNET reviewed his military paycheck and two documents he created at the time of these incidents that detailed multiple workplace concerns he had.

He wasn't the only military veteran to allege difficult working conditions at Amazon. The other two managers CNET interviewed also mentioned brutally long hours, nonstop work and tyrannical bosses.

Additionally, Seth King, a Navy veteran and former Amazon warehouse employee, spoke out last year about Amazon's difficult working conditions, mentioning the isolation from other workers and constant monitoring by supervisors. He said in a Facebook video, released by Sen. Bernie Sanders, a frequent Amazon critic, that the job made him severely depressed. He quit after about three months.

"I was in the Navy for eight years, and there wasn't a single day that I felt as miserable or isolated as I did at Amazon," King said in an interview.

Navy Veteran Experiences Amazon's Horrific Working Conditions The horrific working conditions at Amazon's warehouses took a devastating toll on this Navy veteran. Posted by U.S. Senator Bernie Sanders on Monday, July 23, 2018

A steady drumbeat of troubling stories about Amazon warehouse conditions led 13 mostly Democratic Congress members last month to call on the Department of Labor to investigate Amazon's US warehouses. This group includes presidential candidates Sanders and Rep. Tulsi Gabbard, as well as the so-called "Squad" of progressive congresswomen led by Rep. Alexandria Ocasio-Cortez.

For its part, Amazon has touted its $15 minimum wage, 20 weeks of paid parental leave and $700 million worker retraining program to show its commitment to its more than 650,000 employees. It's also repeatedly said it offers a safe working environment at its warehouses.

We take this allegation seriously as this is not the culture we aspire to create. Rachael Lighty, Amazon

Though USERRA cases are a persistent issue, they've been in decline in recent years. The Department of Labor reviewed 1,098 cases for potential USERRA workplace violations during fiscal year 2017, roughly the same level as the year prior but down from 1,644 in 2012, according to an annual report from the Office of the Assistant Secretary for Veterans' Employment and Training.

Davis, from the VFW, said he's heard less about USERRA violations in recent years as the wars in Iraq and Afghanistan have wound down, reducing the strain of thousands of military personnel serving overseas and away from their civilian jobs.

A competitive environment

Alex Urankar, a regional general manager for Amazon's Fresh and Prime Now businesses in the Northeast, has worked at Amazon for the past four years after serving in the Marines for seven years. He's also led employees in the reserves at the company.

Urankar, who Amazon invited CNET to interview for this story, said he's never heard of any type of pressure put on reserve or part-time military workers while he's been at the company. To the contrary, he added, these employees are typically viewed positively for offering their unique experience.

"I definitely am disappointed to hear those ... individuals feel that way," he said, "but I can tell you from my own experience ... I've never seen or experienced anything like that. It's all been extremely positive."

Thank you to the 17,500 veterans and military spouses now working at Amazon. We set a goal last year to hire 25,000 of these leaders by 2021, and are on track to hire even more. #VeteransDay pic.twitter.com/1tIiSZrRtQ — Jeff Bezos (@JeffBezos) November 9, 2017

Amazon has been recognized for its support of its military workers, receiving the Secretary of Defense's Employer Support Freedom Award last year and landing on the Military Times' "Best for Vets" list for several years. It's also pledged to hire 25,000 veterans and military spouses by 2021 and hosts nearly 100 Warriors@Amazon affinity groups.

Jon Reily, a former Amazon executive in the devices group, said problems like these incidents can arise at Amazon due to a mix of intense pressure to perform, understaffing and high turnover at warehouses. But, he noted, Amazon as a corporation doesn't condone activity like pressuring service members.

"The environment there is so competitive to succeed because there's always someone waiting in the wings to take your job," said Reily, who's now at consultancy Publicis Sapient. "So people bend the rules and take shortcuts to hit their short-term goals."

Being driven constantly to get results, Reily said, "causes people to make poor decisions, like making a water cooler comment to your best employee that he shouldn't serve his country anymore."

Still, even if poor judgment or stress caused these incidents, they may break the law and hurt Amazon's reputation as a top employer of service members.

"Obviously there's some internal training that needs to be conducted on what is legal and what is not," VFW's Davis said. "You don't want the public perception of your company being anti-military."

Originally published Aug. 23, 5 a.m. PT.

Update, Aug. 24: Adds allegations from a third Amazon warehouse manager who reached out to CNET after the initial publication of this story.