The Retail, Wholesale, and Department Store Union (RWDSU) has filed a formal objection to the results of a union election at an Amazon warehouse in Bessemer, Alabama, alleging the e-commerce company threatened to lay off workers. The employees voted against unionizing in an April 9th vote, but the RWDSU is arguing that the results should be set aside because Amazon “created an atmosphere of confusion, coercion and/or fear of reprisals and thus interfered with the employees’ freedom of choice,” the union said in a news release.

“Amazon has left no stone unturned in its efforts to gaslight its own employees,” RWDSU president Stuart Appelbaum said in a statement Monday. “We won’t let Amazon’s lies, deception and illegal activities go unchallenged, which is why we are formally filing charges against all of the egregious and blatantly illegal actions taken by Amazon during the union vote today.”

Amazon said in a statement that it was looking forward to the next steps in the legal process. “The fact is that less than 16% of employees at BHM1 voted to join a union,” the statement reads. “Rather than accepting these employees’ choice, the union seems determined to continue misrepresenting the facts in order to drive its own agenda.”

Workers voted by mail in February and March whether they wanted to join the RWDSU. Of the roughly 5,800 workers at the Bessemer warehouse, 3,041 voted in the election, with 1,798 workers voting against and 738 voting in favor, according to the NLRB. Known as BHM1, Bessmer is only the second US Amazon facility to hold a union vote. If it had been approved, BHM1’s union would have been the biggest group to gain representation in a single NLRB election since 1991.

The RWSDU has a list of 23 objections it has filed with the NLRB. Among other things, the union claims Amazon threatened employees that the Bessemer warehouse would close if they joined a union, and that the company sent an email warning it would lay off workers if the union was voted in.

It also alleges that Amazon installed a ballot collection box in the warehouse parking lot, creating the appearance that the company — rather than the NLRB — controlled the election, and it monitored the collection box via security cameras. An Amazon spokesperson said in a statement emailed to The Verge that the RWDSU allegations about the collection box are not accurate. “We said from the beginning that we wanted all employees to vote and proposed many different options to try and make it easy. The RWDSU fought those at every turn and pushed for a mail-only election, which the NLRB’s own data showed would reduce turnout,” the spokesperson said. “This mailbox—which only the USPS had access to—was a simple, secure, and completely optional way to make it easy for employees to vote, no more and no less.”

The mailbox was a major source of contention during the vote. According to the RWDSU, Amazon pressured workers to bring their ballots to work and put them in the collection box rather than sending ballots by mail and removed workers who supported the union from mandatory captive-audience training sessions. Vice also reported that Amazon sent instructions to employees to vote “no” and told them to use the controversial mailbox.

The union is seeking an investigation into what it says is behavior by Amazon that corrupted the election.