Amazon will face another high-stakes union election at its warehouse in Bessemer, Alabama, in early February, a federal labor agency said Tuesday.

The National Labor Relations Board in November ordered a new vote at the Bessemer facility after finding Amazon improperly interfered in the site’s first union election, which was held last year. In that election, the Retail, Wholesale and Department Store Union (RWDSU) sought to organize workers at the warehouse, but Bessemer workers voted more than 2-to-1 against unionizing.

Amazon workers at the Bessemer site, known as BHM1, will again cast their ballots by mail. The NLRB will begin sending out ballots to workers on Feb. 4, and the votes will be counted on March 28, the agency said.

In granting a do-over, an official at the NLRB said Amazon broke labor laws, pointing to the company’s decision to install a mailbox at the facility, which the RWDSU said created the false appearance that Amazon was conducting the election and intimidating workers into voting against the union.

The official also said Amazon improperly polled workers’ support for the union during mandatory meetings, which were held for several weeks at BHM1, until the time ballots were mailed out to employees.

The second unionization drive will be closely watched by labor groups, lawmakers and other Amazon workers who may be looking to organize their facilities. Major unions such as the International Brotherhood of Teamsters also have their sights set on organizing Amazon.

If an Amazon warehouse were to vote to join a union, it could stand to disrupt the level of control the company has over its employees, such as its ability to set the pace of work and hourly wages.

Elsewhere in the country, Amazon warehouse workers on New York’s Staten Island have filed for a union election, while workers in Chicago have formed a group to organize employees at facilities in the area, called Amazonians United Chicagoland.

For many years, major unions including the Teamsters, the United Food & Commercial Workers Union and the RWDSU have quietly been talking to Amazon workers about organizing, but have faced steep challenges in the U.S. compared to Europe, where unions are common among Amazon’s workforce.

Amazon previously said it disagreed with the NLRB’s decision to order a new election at the Bessemer facility. The company says that unionizing isn’t the best approach for its employees.

Amazon has ramped up its campaign at the Bessemer warehouse by holding so-called captive audience meetings and posting anti-union documents in bathrooms, Reuters reported.

The RWDSU said in a statement that it’s “deeply concerned” by the terms of the new election set out by the NLRB on Tuesday. The union said it didn’t believe a mail-in election could be held fairly and noted it could foster distrust among workers in the process.

“We proposed to the NLRB a number of remedies that could have made the process fairer to workers, which were not taken up in the Notice of Election issued today,” the union said, without detailing specific remedies.

Both Amazon and the RWDSU advocated for an in-person election, but NLRB Region 10 Director Lisa Henderson said in an order accompanying the notice of election that a mail ballot is “the safest and most appropriate method of conducting a prompt election in view of the extraordinary circumstances presented by the pandemic.”

The order also addresses Amazon’s decision to install a mailbox at the site, which was a point of contention during the previous election. The U.S. Postal Service “has moved or will move” the mailbox to a neutral location away from BHM1′s entrance, Henderson said. Neither Amazon or the union will be allowed to put up a tent, banner or sign around it or make any kind of “statement to voters concerning use of the mailbox for the purposes of this election,” she said.

During the seven-week mail-in-election last year, Amazon directed employees to submit their ballots via the mailbox, with a sign on a tent surrounding it reading, “Speak for yourself! Mail your ballot here.”

Amazon workers in Alabama will vote again on whether to unionize next month