NEW YORK (AP) — A hearing officer for a federal labor board has rebuffed Amazon's attempt to scrap a historic union win at a warehouse on Staten Island, New York, handing victory to organizers in what could be a very long battle for recognition.

Thursday's win is a relief for the Amazon Labor Union, the grassroots group of former and current workers whose unexpected victory in April followed weeks of aggressive campaigning from both sides.

"Today is a great day for Labor," Chris Smalls, a fired Amazon worker who now heads the union, wrote in Tweet celebrating the decision.

Shortly after the spring vote, Amazon filed more than two dozen objections with the National Labor Relations Board, claiming it was tainted by organizers and Region 29, the agency's regional office in Brooklyn that oversaw the election. The case was then transferred to another regional office, based in Phoenix, Arizona, at Amazon's request.

The 24-day long hearing, which Amazon had unsuccessfully sought to close to the public, was marked by tense exchanges between attorneys for both sides on what documents could be submitted for evidence and which witnesses could testify.

On Thursday, Lisa Dunn, the agency officer who handled the company's case, concluded Amazon's objections should be entirely overruled and the union be certified as a bargaining representative for the warehouse, a spokesperson for the NLRB wrote in an email.

"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 spokesperson said, offering a summary of Dunn's recommendation.

Amazon Spokesperson Kelly Nantel said the company plans to appeal.

"While we're still reviewing the decision, we strongly disagree with the conclusion and intend to appeal," Nantel said in a statement. "As we showed throughout the hearing with dozens of witnesses and hundreds of pages of documents, both the NLRB and the ALU improperly influenced the outcome of the election and we don't believe it represents what the majority of our team wants."

Amazon, the union and the agency's office in Brooklyn have until September 16 to file any exceptions to the report, which would send the case to the regional director, who will issue an order to certify the election results or order a rerun vote. The company could still appeal that order to the five-person labor board, whose Democratic majority is expected to be sympathetic to the union.

Even when the agency upholds a union victory, experts say companies who don't want a unionized workforce often refuse to negotiate. That move can trigger protracted legal battles in federal court, which some companies could use as a backdoor attempt to thwart labor victories.

In May, the nascent union lost a separate election at a neighboring warehouse, which dampened enthusiasm elsewhere. At the same time, it was devoting more time and resources to defend its initial win from the e-commerce giant.

Other campaigns have kicked off at Amazon warehouses in North Carolina, Kentucky and elsewhere, as workers attempt to gather enough signatures to qualify for a union election. Amazon workers at a warehouse near Albany, New York are slated to vote in their own election in the coming months.