SEATTLE — Amazon improperly pressured Alabama warehouse workers to vote against joining a union and should hold a new election, according to recommendations from a National Labor Relations Board hearing officer.

The Retail, Wholesale and Department Store Union‘s push to unionize a Bessemer, Ala. warehouse earlier this year drew national attention as organizers attempted to crack the United States’ second-largest private employer, which has long come under scrutiny for its labor practices. Other unions and workers across the country were gearing up to follow, and a do-over could re-energize the movement.

That will hinge, however, on a final ruling by the NLRB’s regional director in Atlanta, which oversaw the election. That decision could take several weeks, the agency has said, but could force a new election. And even if the union prevails, it will still have to convince workers who overwhelmingly voted them down.

In a filing Tuesday morning, the NLRB specifically cited Amazon’s efforts to place an unmarked U.S. Postal Service mailbox in front of the warehouse just after voting started, suggesting it could have given workers the impression that the company had a role in collecting and counting ballots. That in turn could have potentially influenced their votes.

That “usurped” the agency’s “exclusive role in administering Union elections,” wrote hearing officer Kerstin Meyers.

“Notwithstanding the Union’s substantial margin of defeat, the Employer’s unilateral decision to create, for all intents and purposes, an on-site collection box for NLRB ballots destroyed the laboratory conditions and justifies a second election,” Meyers wrote.

(Amazon founder Jeff Bezos owns The Washington Post.)

“Throughout the NLRB hearing, we heard compelling evidence how Amazon tried to illegally interfere with and intimidate workers as they sought to exercise their right to form a union,” union president Stuart Appelbaum said in a statement. “We support the hearing officer’s recommendation that the NLRB set aside the election results and direct a new election.”

Amazon countered that the workers “overwhelmingly” opposed unionization, spokesman Ty Rogers said in a statement.

“Their voice should be heard above all else, and we plan to appeal to ensure that happens,” Rogers said.

The NLRB declined to comment on the filing.

Amazon, the nation’s second-largest private employer behind Walmart, has fiercely opposed efforts by its American warehouse workers to organize. But Amazon’s size as well as its role as the nation’s dominant e-commerce operator have made it a high-profile target for labor organizers. A new election would probably spark more high-profile efforts to sway the warehouse staff.

During the nearly two-month mail-in balloting, the union drew support from leaders at the AFL-CIO as well as liberal politicians nationally, including Sen. Bernie Sanders (I-Vt.) and former Georgia gubernatorial candidate and voting rights advocate Stacey Abrams.

The mailbox was the centerpiece of the union’s bid to set aside the election results. The union also alleged the mailbox could have led workers to think Amazon had a role in collecting and counting ballots. In its case, the union cited emails that show Amazon pressing the Postal Service to install a mailbox urgently just as the seven-week mail-in balloting began.

An Amazon executive testified that the company pressed the Postal Service to install the mailbox as a way to make it easy for workers to cast ballots and denied any attempt to influence voting with its location.

Ten days after the votes were counted, the RWDSU filed objections to the agency, alleging that Amazon’s tactics “constitute conduct which prevented a free and uncoerced exercise of choice by the employees.” It argued those actions “constitute grounds to set the election aside.”

That filing led to a nearly three-week hearing in May at the agency’s Atlanta regional office, which oversaw the election. Several workers appeared via video on the union’s behalf, testifying that Amazon’s tactics created an atmosphere of election surveillance. The union argued that perception tainted the election.

Meyers’s 61-page recommendation focuses in large measure on Amazon’s efforts to install the mailbox, as well as the company’s tactics to encourage workers to use it. She wrote that Amazon “created the impression that the mailbox was an ‘official’ polling place” by placing a tent around the mailbox and putting up a banner on it that read “speak for yourself, mail your ballot here.” That undermined the election’s integrity, Meyers wrote.

In the lead-up to the election, the NLRB rejected Amazon’s effort to put a ballot box inside the warehouse. Amazon argued that the election rules didn’t preclude putting a Postal Service mailbox outside the facility, an argument Meyers called “disingenuous,” in her recommendations. And she also criticized Amazon’s claims that the Postal Service installed the mailbox, not the company, as “scapegoating.”

Meyers also found that Amazon’s distribution of union-opposition paraphernalia violated labor law. At anti-union meetings leading up to the election, Amazon handed out “vote no” pins — which featured Amazon’s warehouse mascot, Peccy — and “vote no” tags for workers to hang on the rearview mirrors of their cars. Making anti-union items available isn’t improper, but pressuring employees to make an “open or observable choice” in selecting them is, Meyers wrote. Managers witnessing workers’ decisions whether to take the items “could reasonably cause an employee to perceive that the Employer was trying to discern their support for, or against, the Union,” which constitutes objectionable pressure, she wrote.

The filing wasn’t a complete victory for the union. Meyers, for example, rejected the union’s claim that the company improperly threatened workers that they’d lose pay and benefits if the RWDSU won the election. She found that Amazon’s messaging that employees risked the reduction in benefits with union negotiations was legal.

Meyers also rejected some of the claims made by pro-union workers during the hearing. One employee, Kevin Jackson, testified that he witnessed security personnel opening the mailbox to retrieve its contents. But Meyers wrote that Jackson “appeared uncomfortable and agitated” in his testimony and that the most damning allegations were not corroborated. Jackson’s testimony, she wrote, was “inherently unreliable.”

But the recommendation to set aside the results and hold a new election led the union’s Appelbaum to call Amazon’s tactic’s “despicable” in his statement Monday.

“Amazon cheated, they got caught, and they are being held accountable,” Appelbaum said.

The unionization defeat in April was lopsided, with 1,798 of the more than 3,000 total votes cast opposing unionization. Only 738 workers voted for the union. The margin was larger than the 505 challenged ballots that would have been counted only if they could have affected the outcome. The labor board voided 76 ballots for a variety of reasons.

That loss was a stinging defeat for labor activists, who have complained for years about worker treatment at Amazon warehouses. Amazon had previously beat back a union drive in 2014, when a small group of equipment maintenance and repair technicians at its warehouse in Middletown, Del., ultimately voted against forming a union, following a drive led by the International Association of Machinists and Aerospace Workers.

Despite years of trying, none of Amazon’s warehouse workers in the United States are union members, even though many of their co-workers in Europe, where unions are often seen as part of the cultural fabric of the region, are.