Undercover police in Michigan will no longer be legally allowed to have sex with prostitutes whom they are investigating.

Lawmakers on the state's Senate Judiciary Committee unanimously approved a bill that brought an end to immunity for law enforcement officers for various prostitution-related offences.

The offences related to situations where an officer "engaged in sexual penetration while in the course of his or her duties".

It went on to define "sexual penetration" as "sexual intercourse, cunnilingus, fellatio,
anal intercourse, or any other intrusion, however slight, of any part of a person's body or of any object into the genital or anal openings of another person's body."

Previously, officers could get away with such acts provided they were performed while in the line of duty, in other words: Undercover.

Bridgette Carr, director of the Human Trafficking Clinic at the University of Michigan Law School, told Michigan Radio that the change was important on a symbolic level as much as anything else.

She said: "It's not rampant, but it happens. And I think it says something about us as a community that we would allow this type of exemption for law enforcement, whether it's used very often or not."

Republican Senator Judy Emmons sponsored the bill. Speaking to the Detroit Free Press before it was passed, she said: "We have the dubious distinction of being the last state in the nation to have this law in our books.

"I don't know how anyone could come out and argue against this."

Prostitution is illegal throughout the US, with the exception of eight counties in Nevada that have active legal brothels.