EVANSVILLE, Ind. — The Evansville Police Department claims that customers of several local massage parlors are getting offers for more than what's listed on the establishment's bill of fare.

In a news release issued Tuesday afternoon, police say they'd received complaints that a $40 tip on a $60, hour-long massage would net a customer a sex act at six different parlors. There also were concerns about human trafficking.

Economy:Do proposed improvements to Lloyd Expressway in Evansville go far enough?

Undercover detectives visited each of the parlors, but only directly discovered illicit handiwork at one -- Asian Massage, 2012 E. Morgan Ave. Police say there, a detective was propositioned and touched inappropriately after offering the additional $40.

Police issued a warning to Asian Massage and gave a female employee a prostitution citation.

A call placed to a number listed for Asian Massage seeking comment rang through to an unidentified voicemail message box. A Courier & Press reporter who went to the business Tuesday afternoon found it closed.

"They (Asian Massage) were told, 'Hey, this happened in your business. Don't let this be happening in your business,' basically," Smith said.

The unit conducted surveillance at the following locations between the hours of 10 a.m. and 10 p.m starting May 8: First Ave Massage and Spa, Asian Massage, Beijing Spa, Lilac Massage, Royal Spa, and Sunrise Spa.

Indiana:Hoosier foster kids file class action suit in Evansville's U.S. District Court against DCS

The unit noticed most activity occurred between the hours of 4 p.m. and 8 p.m. Police say only men visited the parlors during this time frame. Detectives would conduct roadside interviews with clients after they left the business.

Police say nearly 90 percent of all male customers interviewed admitted they paid $60 for an hour-long massage and a additional $40 for a sexual act. All customers interviewed were documented and released.

Smith he did not know the exact number of men interviewed. Smith said citing the men during an undercover investigation may have disrupted the process.

Undercover detectives later went into the businesses with marked currency. They received massages and then attempted to solicit sexual favor for tips. Before concluding the investigation May 15, detectives discovered the citizen complaints were correct but did not find evidence that involved females were victims of human trafficking.

"When we received citizens complaints about the inappropriateness ... of course the hot topic in the country right now is human trafficking," said EPD Sgt. Phil Smith. "Some of those complaints were about human trafficking. Of the individuals interviewed, we did not discover anyone that was a victim of human trafficking."

Breaking news:Girl Scout killed at Camp Koch identified as Jasper girl

Sgt. Todd Mattingly said each parlor will be monitored periodically and issued citations and city ordinances for employers and employees without massage licenses.

"Each parlor will continued to be monitored and the appropriate citations will be issued if they are found in violation," police said in the news release. "The Safety Board will seek to suspend or revoke the massage/clinic license if they employ an unlicensed employee, and after conducting a public hearing on the matter."