CHICAGO (CBS) – It’s been a long hot summer for the Chicago Police Department, trying to get a grip on a spike in deadly gang violence.

CBS 2 has learned dozens of Chicago cops will be leaving town this week, to head to the Democratic National Convention in Charlotte, N.C.

CBS 2’s Brad Edwards reports both police brass and the police union were defending the decision to have officers work security perimeter details in Charlotte.

They said it won’t affect the number of street cops here in the city of Chicago, since the officers headed to Charlotte are there on their own time.

Still, the move raised eyebrows on the heels of Mayor Rahm Emanuel asking for federal help to police the streets in two high-crime districts on the South Side.

In part, having Chicago cops helping with security at the DNC is payback to Charlotte, for sending some of its officers to assist with security at the NATO Summit at McCormick Place in May.

No one was providing specifics on how many Chicago officers were working at the DNC, but it was no more than 50.

Chicago Fraternal Order of Police spokesman Pat Camden said, “these officers are on their days off, and they wouldn’t be on the street. This has no direct affect on manpower. That said, we do need more police officers, but they need to be hired on full time.”

City officials said the DNC likely would pay for the use of the Chicago officers to work security.