Results from union elections at Amazon.com Inc.'s warehouses in New York and Alabama started coming in on Thursday, with early counts showing a potential landmark victory for organized labor at a Staten Island warehouse.

An early tally in Alabama indicated a close vote that could hinge on challenged ballots, a much different situation than last year when Amazon won by a 2-1 margin.

If final results show workers at either location voted for a union, it would be a historic first at the online retail giant, which has long opposed any effort to organize its employees.

With about 575 ballots counted from workers at a warehouse in New York City's Staten Island, the vote was 325-250 in favor of creating a union with many more ballots left to count, according to a Reuters tally of the count overseen by the National Labor Relations Board (NLRB).

With more than 500 ballots counted from workers in Bessemer, Alabama, there were about 30 more anti-union ballots. In that contest the union has said there are 2,375 ballots total, with hundreds contested.

Neither the union nor labor board has said how many ballots were received in Staten Island.

As the second-largest U.S. private employer, Amazon has long been a focus for labor advocates who hope that a single union victory will spark organizing efforts across the country.

The vote counts starting Thursday may not result in a final determination. Ballots that either side challenged as invalid would be addressed after the count in the event of a close election and could alter the outcome. In addition, parties can object to conduct around the vote that could set aside the results as happened last year in Alabama.

A simple majority of votes cast is needed to win.

Workers at the company's JFK8 warehouse in Staten Island voted in person over a six-day period that began on March 25. They are voting on whether to form a new union, the Amazon Labor Union.

A rerun of last year's failed union organizing campaign at Amazon's warehouse in Bessemer, Alabama, concluded on March 25. Workers there voted by mail. They are voting whether to join the Retail, Wholesale and Department Store Union.

The NLRB found that Amazon improperly interfered in the original contest, which the company won by a 2-1 margin.