San Francisco's police union is the sole reactionary conservative political voice in a city where the political spectrum ranges from progressive to liberal.

Perhaps it's not shocking, given the history of black people and police in America, that many major cities have mutiple police unions or fraternal organizations that are divided along racial lines.

During the 1960s, when police organizations were often being created to combat the demands of people of color—an end to brutality, equal rule of law, name tags, civilian oversight—the few black police officers in Chicago banded together to form the Afro-American Patrolmen's League. It was one of the first black police unions. "King had been assassinated, Malcolm X had been assassinated. What it pointed out was the need for the black community to be protected. We saw all this killing going on," said Edward Palmer, the AAPL's founder.

In most major American cities, these divisions still exist. As recently as 2014, the black then-chief of the Dallas Police Department proposed doing away with the segregated system, only to be shouted down by the city's various unions. Many black police unions have publicly disavowed the endorsement of Trump made by the National Fraternal Order of Police, the largest police union in the country with "lodges" in Chicago, Philadelphia, Dallas, Miami, and Newark.

A review of over 80 big-city police union contracts and 13 state "police bills of rights" by activist group Campaign Zero found that nearly 90 percent contain language barring police officers from true accountability in some way.

As the New Yorker's James Surowiecki writes, "All labor unions represent the interests of the workers against the bosses. But police officers are not like other workers: they have state-sanctioned power of life and death over fellow-citizens."

Related: Chicago's police union is particularly bad. The contract includes language making it incredibly difficult to fire officers, even for heinous acts, and hamstrings police oversight agencies. As TMN's Sam Stecklow reported earlier this year, the Chicago Fraternal Order of Police until recently regularly distributed misinformation about the victims of police shootings from the scene of the crime, to stave off lawsuits from families and charges from prosecutors, and have been at the center of efforts to destroy police misconduct files dating back to 1967.

After the National Fraternal Order of Police, the nation's largest police union, endorsed Donald Trump, its labor bretheren are publicly pushing back. The FOP “has publicly turned a blind eye to the minority community as a collective,” the president of the Coalition of Black Trade Unionists told BuzzFeed News.

This is just the latest in a long line of right-left disputes between police unions and traditional labor.