A US official Thursday rejected Amazon's efforts to overturn a worker vote in favor of unionization at a New York warehouse, dismissing the retailer's election complaints as groundless.

Lisa Dunn, a hearing officer with the National Labor Relations Board, who oversaw a 24-day hearing on Amazon's complaints earlier this summer, concluded the firm's objections "should be overruled in their entirety," according to a statement released by the NLRB's press office.

"The Employer has not met its burden of establishing that Region 29, the Petitioner, or any third parties have engaged in objectionable conduct affecting the results of the election," the NLRB said, adding that Amazon should recognize Amazon Labor Union as bargaining representative for the facility, JFK8.

Amazon has until September 16 to contest Dunn's conclusion. The NLRB regional director would then decide whether to rerun the election or certify the vote in a determination that could be appealed to the board itself.

Dunn's decision is the latest development since Amazon Labor Union's (ALU) shock victory in April in which New York workers voted to establish the first Amazon union in America at a facility in Staten Island, New York.

Amazon has asserted that union members intimidated workers into voting for the union and that local NLRB staff were biased against the retail colossus.

But the ALU has said these claims are groundless, accusing the company of using delay tactics to put off talks on a on a contract in an attempt to quash the labor movement.