Amazon Labor Union workers at Staten Island's JFK8 building celebrated a major victory on Wednesday when a federal regulator officially certified their group's historic election victory.

The National Labor Relations Board's Region 28 Regional Director Cornele Overstreet issued a decision agreeing with another NLRB official's recommendation that Amazon’s objections to a successful April unionization vote at one of its Staten Island warehouses be rejected, and that the union be certified. The ruling officially certified the union and means Amazon must begin bargaining in good faith with the union or request a review of the decision by Jan. 25.

"We beat @amazon fair and square now is time to sign a CONTRACT!" tweeted Chris Smalls, who led the Amazon Labor Union's grassroots efforts on Staten Island.

Derrick Palmer, vice president of the ALU, also tweeted, "The ALU @amazonlabor is officially a certified union ‼️This is a huge moment for the labor movement! We will continue fighting for a better contract for all @amazon workers across the world."

The JFK8 vote at the end of March showed a majority of the 8,325 eligible voters cast ballots in favor of the Amazon Labor Union. Amazon had contested those results soon after, arguing that the Amazon Labor Union engaged in "conduct warranting setting aside the election and conducting a rerun election," the NLRB said.

Wednesday's decision, the NLRB said, found that Amazon did succeed in proving that case, and must now come to the bargaining table with union leaders.

The NLRB definition of bargaining in good faith says "this duty encompasses many obligations, including a duty not to make certain changes without bargaining with the union and not to bypass the union and deal directly with employees it represents."

Amazon said it still had plans to appeal, however.

“We knew it was unlikely that the NLRB Regional Office would rule against itself, and intend to appeal," said Amazon spokesperson Kelly Nantel. "As we’ve said since the beginning, we don’t believe this election process was fair, legitimate, or representative of the majority of what our team wants.”

This story has been updated with comment from Amazon.