CHICAGO (CBS) — Chicago police and city officials have been cracking down on massage parlors running afoul of city regulations, and have busted six business for prostitution.

The Chicago Police Department and the city’s Department of Business Affairs and Consumer Protection called the effort “Operation Hot Towel,” because when undercover cops investigating prostitution were offered sex, they would ask for a hot towel, and other officers would swoop in to make arrests.

“A total of 84 locations were inspected, and about 20 of these locations involved undercover officers,” CPD Organized Crime Bureau Chief Anthony Riccio said.

Only six were busted for prostitution, but most parlors that were inspected were found to be in violation of various city ordinances, such as operating without a license.

Ald. Matt O’Shea (19th) said he will introduce a proposal to target the owners of massage parlors that rely on prostitution, instead of the employees, who he said are often immigrants and the victims of human traffickers.

“We must change the way our society looks at this issue,” he said. “These seemingly innocent storefronts erode the quality of life, and represent a horrific fate for those forced to work in them.”

The ordinance would raise the minimum age from 15 to 18 to work in a massage business, and would increase prostitution-related fines from $500 to as much as $5,000.

BACP officials said 11 parlors were issued cease-and-desist orders, and 10 were shut down, including Seven Heavens Spa, at 1026 N. Ashland Av., which allegedly reopened after the city ordered it closed.

Now, the owner faces as much as $37,000 in fines.