Amazon.com Inc. alleged, without providing evidence, that the union that Staten Island workers voted to join had threatened staff to vote in favor of organizing, as part of objections the retailer is filing to last week's election.

The group, known as the Amazon Labor Union (ALU), dismissed the allegations as false and said it was confident they would be overruled.

The U.S. National Labor Relations Board on Thursday granted Amazon extra time to substantiate its objections, among them that the ALU interfered with workers waiting in line to vote, according to filings.

Some 55% of voting employees at Amazon's JFK8 warehouse in the New York City borough of Staten Island decided to form the company's first U.S. union, a milestone for labor organizers.

Eric Milner, an attorney representing the ALU, responded to Amazon's claims by saying the union looked forward to having the truth come out.

"To say that the Amazon Labor Union was threatening employees is really absurd," he said. "The Amazon Labor Union is Amazon employees."