Chipotle is closing a Maine store that had been leading efforts to unionize the chain.

Employees at the Augusta, Maine, Chipotle filed a petition with the National Labor Relations Board in June asking to hold a union election at the store. It was the first of the Mexican food chain’s stores to file such a petition, according to NLRB filings.

The NLRB had scheduled a hearing today on Chipotle’s objections to the union election. But early today, Chipotle announced it was permanently closing the store.

Labor organizers say they will fight the closure. They say Chipotle is retaliating for their unionization efforts and trying to send a message to other stores that might try to unionize.

“We’re calling this union busting 101,” said Jeffrey Young, an attorney for Chipotle United, the group that was trying to unionize the Augusta store.

But Chipotle said the closure was due to staffing issues and not related to union activity.

“Chipotle respects our employees’ rights to organize,” said Laurie Schalow, Chipotle’s chief corporate affairs officer, in a statement.

The closure comes amid a broader unionization push across the country. Chipotle United has said it was inspired by labor organizers at Starbucks, who have unionized more than 180 U.S. stores since late last year. Amazon workers at a warehouse in New York also voted to unionize in the spring

Newport Beach, California-based Chipotle said the Augusta store had been closed to the public since June 17 because of staffing issues. The company said it was facing “excessive” absences and lack of availability from existing staff and was having a hard time finding managers for the store.

Chipotle said the store’s workers will receive severance pay and assistance finding new jobs. Young said there were about 20 workers at the store.

Young said inadequate staffing at the store is one of the chief complaints of union organizers. Chipotle United plans to ask the NLRB to file an injunction that would prevent Chipotle from closing the Augusta store and allow the union election to go forward.

Starbucks has also been criticized by labor organizers for closing stores that have unionized, including a store it shuttered last month in Ithaca, New York.

Unlike Starbucks’ unionization effort, which is backed by the larger Workers United union, Chipotle United is an independent organization.

But big unions are also backing organizing efforts at Chipotle. The Teamsters filed a unionization petition with the NLRB this month on behalf of workers at a Chipotle store in Lansing, Michigan. There is also a group called Chipotle Workers Union that is backed by the Service Employees International Union.

Chipotle Mexican Grill Inc. owns and operated nearly 3,000 U.S. stores.