SEATTLE — The union that lost its bid to represent Amazon warehouse employees in Bessemer, Ala., earlier this month is now seeking to overturn the election results, claiming in a legal filing that the e-commerce giant improperly pressured workers to oppose unionization.

The Retail, Wholesale and Department Store Union filed its objections with the National Labor Relations Board on Friday, a move that triggers a hearing process to resolve its claims. Labor laws require the agency to set that hearing within 15 business days of the vote tally, or by April 30. If the union succeeds, the labor board could call for a new election.

The union said it would file objections when it lost the high-profile vote April 9, a lopsided defeat in which 1,798 workers opposed unionization and 738 supported it. That margin of victory left another 505 ballots uncounted because they would not have changed the outcome.

The RWDSU alleged Amazon’s tactics in the election “constitute conduct which prevented a free and uncoerced exercise of choice by the employees,” adding that the actions “constitute grounds to set the election aside.”

Amazon spokeswoman Heather Knox questioned the RWDSU’s challenge in the aftermath of the Bessemer staff overwhelmingly opposing unionization.

“Rather than accepting these employees’ choice, the union seems determined to continue misrepresenting the facts in order to drive its own agenda,” Knox said in an emailed statement. “We look forward to the next steps in the legal process.”

(Amazon chief executive Jeff Bezos owns The Washington Post.)

While many of the union’s allegations echo claims it made during the course of the organizing drive, it also made a series of new ones. In its filing, the union accused Amazon of firing a union supporter “for passing out union authorization cards in non-working areas.” The RWDSU also accused the company of disciplining “an outspoken supporter” of the union for challenging Amazon’s arguments during mandatory meetings. The union didn’t name either worker or disclose the specific discipline.

The RWDSU included a charge it previously leveled at Amazon over a U.S. Postal Service mailbox that popped up in front of the warehouse just after voting started. The union obtained emails through Freedom of Information Act requests that show that Amazon employees pressed the Postal Service to install a mailbox just as the seven-week mail-in balloting began.

In its filing, the union argued the mailbox, which has no U.S. Postal Service markings, created the impression that Amazon had a role in collecting and counting ballots, potentially influencing their votes. And it noted that the NLRB, which set the rules for the election, rejected Amazon’s request to put ballot boxes at the warehouse for in-person voting. The labor board cited concerns about the safety of Amazon workers and agency staff members during the coronavirus pandemic.

Amazon has previously defended the mailbox placement, saying it made voting easier for workers, and that only the Postal Service had access to it.

The union also claimed in its filing that Amazon’s successful effort to convince local county officials to change the timing of a traffic light just outside the warehouse improperly inhibited its ability to engage with workers at the end of their shifts. Amazon has said it requested the change to improve traffic flow.

And the union alleged that a financial offer Amazon made to lure unhappy workers to quit amounted to an improper incentive to weed out pro-union employees. Amazon has countered those charges, noting that it began offering financial incentives to quit in 2014 and extends the initiative to its entire North American warehouse staff.

The RWDSU filing also claims Amazon threatened layoffs, and even closing the warehouse, if workers voted for union representation. It alleges Amazon “disparately enforced” its pandemic-related social distancing policy in the warehouse, permitting anti-union staff to campaign but preventing pro-union workers from having the same sort of access.