(Bloomberg) -- Amazon.com Inc. violated federal labor laws when it prevented off-duty employees from using workspaces for union organizing, US labor prosecutors alleged in sweeping new complaints, escalating their standoff with the country’s second-biggest private employer.

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The National Labor Relations Board announced the allegations Tuesday, saying Amazon selectively prohibited employees from accessing nine warehouses in Alabama, Illinois, New York, Pennsylvania and Wisconsin. The complaints seek to force Amazon to allow employee access to facilities for organizing purposes and to train staff about related procedures.

The online retailer, which relies on a blue-collar workforce to pack and ship customer orders, is increasingly clashing with labor organizers around the country. The NLRB, which enforces federal labor laws, has more than 180 open or settled unfair labor practice cases filed against Amazon in 22 states.

Amazon spokesperson Eileen Hards said that Tuesday’s complaints are “completely without merit and we look forward to showing that through the legal process.”

Bloomberg reported on Monday about one of the complaints, which pertains to an Amazon warehouse in Staten Island. At that site, workers voted last year to be represented by the Amazon Labor Union.

Amazon also has faced off against the Retail Wholesale and Department Store Union, or RWDSU, in an election that is still being investigated. The International Brotherhood of Teamsters, meanwhile, announced in April that a group of contract Amazon delivery drivers in California joined its union.

Complaints issued by NLRB prosecutors are heard by agency judges, whose rulings can be appealed to the labor board members in Washington, and then to federal court. The agency has the authority to order employers to reinstate workers and change policies, but not to fine them with punitive damages or hold executives personally liable for violations.

In the RWDSU case, the union is seeking to represent workers at an Amazon warehouse in Bessemer, Alabama. Federal officials determined that Amazon’s conduct during a vote there in 2021 made a fair election impossible, but a rerun election hinges on contested ballots.

--With assistance from Josh Eidelson.

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