"All told, Whole Foods terminated workers in at least six states for wearing BLM apparel, according to a complaint brought by the National Labor Relations Board...."

"NLRB officials are now prosecuting Whole Foods, seeking a change in policy and reinstatement for the workers. The company’s defense has yielded one of the stranger spectacles in contemporary US labor law. Whole Foods not only denies doing anything wrong, it’s also effectively putting BLM on trial. 'At one point, President Trump referred to Black Lives Matter itself as, quote, "a symbol of hate," and like it or not, a significant number of the former president’s supporters share his view,' company attorney Michael Ferrell said during his opening statement at the NLRB trial in Boston this spring. Yes, Ferrell said, Whole Foods believes Black lives matter, but the BLM movement is 'controversial,' its protests have been marked by looting and violence, and the company had good reason to worry that stores would become dangerous if workers were allowed to show their support on the job. If Whole Foods is forced to permit employees to wear BLM logos, Ferrell said, then why not let them wear Confederate flag masks, or go shirtless?...'It is for Whole Foods’ leadership to decide,' Ferrell said. “It is not for the hourly store team members.' That’s a point the NLRB’s top prosecutor, General Counsel Jennifer Abruzzo, is eager to litigate.... 'I’m not sure that all circuit court judges, or even district court judges for that matter, fully understand all the nuances of labor law,' she says. 'We try to educate them as best we can.'"

From "Washington’s Top Labor Prosecutor Battles Whole Foods Over Black Lives Matter Masks/Jennifer Abruzzo, general counsel at the NLRB, is seeking a ruling that would give US workers something more like free speech" (Bloomberg).

I'm not sure what "would become dangerous." Is it that workers who didn't choose to wear the slogan could be threatened? Is it that customers might go ballistic? Was Ferrell talking about physical danger or some sort of emotional "danger"? Some people might feel hated when they read the slogan "Black Lives Matter" — is that a "danger"? I'm thinking of the vogue concept that words are violence. But stepping back from that puzzling word "danger," I can see that management has to worry that some customers may sense hostility and decide to shop elsewhere. The mask itself already embodies the hostility of the deadly virus. Writing an aggressive — or merely confusing — message on the mask has a synergistic effect.