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AUGUSTA, Maine (AP) — Chipotle Mexican Grill violated federal labor law by closing a Maine restaurant where workers sought to unionize, the National Labor Relations Board said.

Employees at the Chipotle in Maine’s capital city of Augusta filed an NRLB petition in June asking to hold a union election, becoming the first of the Mexican food chain’s restaurants to file such a petition. The following month, Chipotle announced it was permanently closing that location.

Workers accused Chipotle of retaliating and sending a message to other stores that might try to unionize.

A complaint filed Thursday by the National Labor Relations Board seeks to force the company to reopen the restaurant, reinstate the workers and provide back pay.

Lisa Schalow, Chipotle’s chief corporate affairs officer, insisted the closing had nothing to do with union activity.

“We respect our employees’ rights to organize under the National Labor Relations Act and are committed to ensuring a fair, just, and humane work environment that provides opportunities to all,” she said in a statement.