Say you're a cop in Michigan and you get caught having sex with a prostitute while on duty. Do you go to jail? No. Are you even charged? Again, no. Michigan is believed to be the only U.S. state that looks the other way if police have sex with prostitutes during sex trafficking investigations.

That may change under a bill Rep. Gary Glenn, a Republican from Milford, is drafting with the help of Bridgette Carr, a professor and director of the University of Michigan's Human Trafficking Clinic. Carr said an exemption that allows police offices impunity from prosecution isn't often used, but "it happens." Michigan has one of the highest sex-trafficking rates in the country, according to data from the National Human Trafficking Resource Center. Carr and others say the exemption for police compounds the problem because prostitutes often are victims of the sex trade.

Hawaii phased out its impunity clause in 2014 after concerns were raised that police may have been abusing it. National debate over the Aloha State's exemption put Michigan's law on Carr's radar. She told Michigan Radio "a number of folks in the human trafficking community were upset that Michigan retained the exemption."

"The reason the law is structured the way it is is because of the way the prostitution laws are written," she said. "So for law enforcement to have any power to investigate with immunity, they got all the power. And no one thought to go back and carve out a prohibition against sexual intercourse." Carr said her research showed the exemption isn't widely used by cops and prosecutors, but some question why changing the law is necessary.