(Reuters) - Roughly 500 ballots submitted in Amazon.com Inc’s landmark union election have been challenged in a contest that will determine whether an Alabama warehouse becomes the online retailer’s first organized workplace in the United States, people familiar with the matter said. With about half of roughly 3,200 ballots counted, the election is currently poised to result in workers rejecting a unionization push by a more than 2-1 margin, potentially dealing a blow to organized labor. The challenged ballots could take on significance if the union meaningfully closes the gap when additional votes are counted. The U.S. National Labor Relations Board would adjudicate the disputed ballots if necessary to determining the outcome. Representatives for Amazon and the Retail, Wholesale and Department Store Union (RWDSU) challenged the ballots during closed-door election proceedings that lasted more than a week before U.S. officials began publicly counting votes. They were able to question ballots on suspicion of tampering, a voter’s eligibility and other issues. It is not clear how many votes each side challenged. The union on Wednesday said hundreds of ballots were contested, mostly by Amazon. The company has not commented on that claim. Of the 3,215 ballots received, workers have so far voted 1,100-463 against forming a union at the warehouse in Bessemer, Alabama, after several hours of counting on Thursday. The vote count will resume at 8:30 a.m. CT (1330 GMT) on Friday. Unionizing Amazon, the second-largest private employer in America, has been a goal for the U.S. labor movement, which is aiming to reverse long-running declines in membership. Union membership fell to 11% of the eligible workforce in 2020 from 20% in 1983, the U.S. Bureau of Labor Statistics has said.