The police union ordered and distributed the masks emblazoned with black-and-white American flag with a blue stripe across the middle. The symbol is associated with the Blue Lives Matter movement, a display of unity among police officers in response to the national Black Lives Matter movement.
A retired civil rights lawyer told the San Francisco Chronicle the masks, which also includes the logo for the San Francisco Police Officers Association, violate a long-standing policy that bars police from expressing political opinions while wearing their uniforms.
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"The thin blue line is a political symbol," John Crew said. "And it's a POA-branded mask. It's like wearing a political button."
The police union president, Tony Montoya, said the union had shown the masks to Scott's command staff, and several of them had asked for more than one. The blue line "represents law enforcement's separation of order and chaos," he said.
The Associated Press contributed to this report.