INDIANAPOLIS -- Thirteen Indianapolis massage parlors were targeted in a multi-agency sweep on Monday as part of the city's effort to curb prostitution at those businesses.

The parlors were targeted because of the nature of their advertising, the number of prior police runs and arrests there, 6News' Jack Rinehart reported.

"We're hearing from IMPD that there is human trafficking ofetn in these locations," says Katie Bannon, head of the Nuisance Abatement Office for the Indianapolis Department of Code Enforcement.

Six of the parlors had prostitution arrests last week. Some of the businesses had multiple violations, including a lack of proper business licenses and licenses for therapists. Some violated the fire code, along with zoning issues and sign violations.

The city hopes that heat from various regulatory agencies will force the illicit businesses to shut down.

Comprehensive cases are being put together, with fines and penalties that are likely to be imposed running into the thousands of dollars.

Police said the parlors advertise in Nuvo and are talked about on various local Web sites in which people seek sex in exchange for money.

The city doesn't know how many illicit massage parlors there are in Indianapolis because they pop up in different places frequently and without regulatory approval.

There was a prostitution arrest at DX Spa, in the 5100 block of South Emerson Avenue last week.

An Anderson man, who was getting a massage at the spa when police rushed in, was ordered by police to put his clothes on.

"When you see the police come in, you normally think you're in trouble. I made a mistake," he offered on a condition of anonymity.

Officials said the business didn't have proper licenses, that its signs were in violation of city code and that there were lighting issues and fire code violations in the building.

Officials said some of the violations can be charged per day and will quickly run into the thousands of dollars.

The city of Indianapolis licenses 27-different businesses and the Department of Code Enforcement has initiated a big push to regulate and enforce each one.

"We're going to take an aggressive approach. We're going to create a case that's really going to bring everything together," says Bannon.

"They just can't continue to operate in the city if this is how they're going to operate," she said.

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