Richmond, Calif., Police Chief Chris Magnus, who gained nationwide attention for  holding a sign reading "Black lives matter" at a peaceful protest in his city, was criticized by his department's rank-and-file Friday for doing so in uniform, reports the San Francisco Chronicle .

The Richmond Police Officers Association said members were not upset by the message, but by the fact that Magnus was wearing his uniform when he attended a Tuesday demonstration on Macdonald Avenue. The message on his sign is one of the rallying cries that emerged after grand juries in Missouri and New York declined to indict white police officers for killing two unarmed black men.

The union said the chief's actions violated the state's Government Code, which states that "No officer or employee of a local agency shall participate in political activities of any kind while in uniform."

Magnus said Friday, "When did it become a political act to acknowledge that 'black lives matter' and show respect for the very real concerns of our minority communities? This should not be about 'us versus them.' It should be about finding ways to build bridges and address the schism that exists between many of our residents and police."

Alison Berry Wilkinson, an attorney for the Richmond police union, countered, "If his officers did the same thing, on either side of the issue, they would be disciplined."