Employees in Bessemer, Alabama held a vote in early April as to whether the RWDSU would represent them. In the end, only 738 of approximately 3,000 votes were in favor of representation, killing the most high-profile union push in the company's history.
The RWDSU responded by filing an objection with the National Labor Relations Board (NLRB) that alleged Amazon interfered in the process, creating "an atmosphere of confusion, coercion and/or fear of reprisals" during the run-up to the vote.
The union is requesting a hearing on the matter with the NLRB.
"Workers fighting for a voice and fair treatment in the workplace will await the results of the hearings on the objections to determine the final outcome of their union vote," the union said in a statement posted on its website.
"After enduring an intensive anti-union campaign designed by Amazon to intimidate and manipulate, workers are seeking the chance to finally have a right to fair representation, a seat at the table and a real chance to fix the litany of issues that workers at Amazon have faced for far too long," the union continued.
Stuart Appelbaum, the union's president, said that Amazon "left no stone unturned in its efforts to gaslight its own employees."
In a statement to FOX Business, Amazon said the RWDSU is refusing to accept the results of the vote.
"The fact is that less than 16% of employees at BHM1 voted to join a union," Amazon said, which refers to its warehouse outside Birmingham as BHM1. "Rather than accepting these employees’ choice, the union seems determined to continue misrepresenting the facts in order to drive its own agenda. We look forward to the next steps in the legal process.
Both Amazon and the RWDSU waged aggressive campaigns ahead of the vote at the 6,000-worker Bessemer warehouse.
Amazon acknowledged after the results that it is far from a perfect company but said it works hard to listen to employees, "take their feedback, make continuous improvements" while investing in greater pay and benefits.
Now that the election is over, Amazon said "there's an opportunity to move from talk to action across the country" in terms of approving wages and benefits for millions of Americans.
"There are 40 million Americans who make less than the starting wage at Amazon, and many more who don't get health care through their employers, and we think that should be fixed," the company said.
The Associated Press contributed to this report.