Workers at an Amazon warehouse in Alabama have begun voting on whether to form the first American union at the e-commerce giant, an effort that could pave the way for further unionization in the United States at one of the world's most powerful companies.

Amazon is the second-largest employer in the US with an 800,000-strong workforce, most of whom are "essential workers" who cannot do their jobs from home during the coronavirus pandemic.

'There have been a series of protests around the United States on safety and working conditions at Amazon, with the pandemic increasing pressure on its distribution network even as profits soar.

Employees at its BHM1 facility in Bessemer, Alabama, notified authorities of their plan to unionize in November.

"Working at Amazon is supremely dangerous. The record on Amazon's deadly and dehumanizing working conditions is well established," the pro-union campaign website says.

"Amazon warehouse workers face outrageous work quotas that have left many with illnesses and lifetime injuries."

In addition to safety, the campaign is urging employees to vote in favor to improve procedures covering grievances, discipline and termination.

Ballots started to go out by mail on Monday to the 5,800 workers at the Bessemer warehouse, with voting to continue through March 29 under an order from the National Labor Relations Board.

The count is expected to begin March 30.

The campaign is the most serious since 2014 when Amazon workers at a Delaware facility voted against a union, and could spark further efforts to unionize hundreds of thousands of employees in the United States.

Unlike in the United States, Amazon workers in many other parts of the world are unionized.

'An abusive relationship'

Helmed by the world's richest person Jeff Bezos, Amazon does not officially oppose unions but it has campaigned against the move within the Bessemer workforce.

In addition to flyers posted in bathrooms, it has held meetings for workers to make the case against unions and launched a website called "#DoItWithoutDues".

"Why pay almost $500 in dues? We've got you covered with high wages, health care, vision, and dental benefits, as well as a safety committee and an appeals process," the website says, though it notes the benefits only apply to full-time employees.

"There are no weekly meetings to go to over how you're feeling, and how you are mentally handling the pandemic," Joseph Jones, a part-time worker at the Bessemer warehouse, told AFP.

"But... we have mandatory meetings to go to over how bad a union would be.

"It's almost like an abusive relationship where the abuser keeps saying, 'I'm sorry, don't go to the police, I will be better... we don't have to go to a third party,'" Jones added.

Amazon has argued, however, that it pays its employees more than double the minimum wage in Alabama.

Company spokeswoman Heather Knox said more than 90 percent of the Bessemer warehouse employees said they would recommend Amazon to their friends as a place to work.

Amazon also says it has invested billions in worker safety even as it has boosted the number of its employees.

Backed by Bernie

It is unclear so far how many of the Bessemer employees support a union.

If a majority vote in favor, they will automatically be represented by the Retail, Wholesale and Department Store Union (RWDSU) but will only become full members after approval of a new company contract, negotiated between the union and Amazon.

The firm had decided on a minimum wage of $15 per hour for all of its US employees, a measure that was welcomed by the federal government and unions after months of criticism and political pressure over safety and working conditions.

The Alabama union effort has gained nationwide attention and could inspire other such campaigns at other Amazon facilities if successful.

"It cannot be overstated how powerful it will be if Amazon workers in Alabama vote to form a union," US Senator and longtime labor rights campaigner Bernie Sanders tweeted Saturday.

"They are taking on powerful anti-union forces in a strong anti-union state, but their victory will benefit every worker in America. I'm proud to stand with them."