(Bloomberg) -- Amazon.com Inc.’s Whole Foods Market illegally banned employees from wearing “Black Lives Matter” masks and punished workers who did, U.S. labor board prosecutors alleged.

The grocery store chain maintained appearance rules at U.S. locations to prohibit staff from displaying Black Lives Matter messages on their apparel, the National Labor Relations Board’s San Francisco regional director wrote in a complaint issued Friday on behalf of the agency’s general counsel. The filing also accuses the company of firing, sending home and otherwise punishing employees around the country during 2020 for wearing apparel such as BLM masks or pins.

“Our dress code policy is designed to ensure we are giving Team Members a workplace and customers a shopping experience focused entirely on excellent service and high-quality food,” Whole Foods said in a statement. “We do not believe we should compromise that experience by introducing any messages on uniforms, regardless of the content, that shift the focus away from our mission.”

Federal labor law protects workers’ right to engage in collective action related to workplace issues, and the Democrats leading the NLRB under President Joe Biden have signaled they take a broader view of that protection than their predecessors under former President Donald Trump. The agency’s lawyers, in Friday’s complaint, said that Whole Foods, by banning Black Lives Matter messages, was restricting employees from exercising their legal rights to participate “in concerted activities for their mutual aid and protection.”

Employees in California, Massachusetts, New Hampshire, Pennsylvania, New Jersey, Virginia, Maryland, Georgia, Washington and Indiana were told at various times in 2020 to remove Black Lives Matter apparel or punished for wearing it, according to the complaint.

“Issues of racial harassment and discrimination are central to employees’ working conditions, and the National Labor Relations Act protects employees’ right to advocate for change,” Jill Coffman, the NLRB regional director in San Francisco, said in a statement. “Through this complaint, we seek to enforce the act and protect workers’ rights to speak up about these important issues.”

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