It's against the law for police officers to appear at political campaign events in uniform to endorse candidates, and for good reason. That's been the law in New York for more than 40 years, and for good reason: having uniformed officers endorse a politician at a campaign event can either give the candidate an aura of support from the government itself or make people afraid to oppose the police choice, which is inappropriate in elective politics.

Hempstead Town Supervisor Kate Murray received the endorsement of the Nassau Police Benevolent Association and the detectives union in her run for district attorney at an event Monday outside Nassau County Court in Mineola. About 10 uniformed officers, some holding "We Support Kate" signs, were at the event with union leaders.

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In 2014 the state Board of Elections reaffirmed the law, ruling: "The use of the uniform as a prop adds the weight of the police office and accomplishes the very evil which . . . [the election law] would avoid."

ColumnNassau cop unions promote Murray for new ballot line

Now the Nassau County Police Department has launched an internal investigation into the officers' participation.

PBA president James Carver says he was unaware of the law, which is possible but also surprising. Carver's knowledge of everything related to the rights and regulations that apply to cops is generally encyclopedic. He also says the appearance of uniformed cops at campaign events is not new and has happened in support of candidates of both parties, including Kathleen Rice, a Democrat who left the post after winning a seat in Congress.

What's clear, now that the unions, officers and candidates know the law, is that it shouldn't happen again, and particularly not at the events of politicians campaigning for the job of upholding the law.