HONOLULU (AP) — Honolulu police officers are urging lawmakers to keep an exemption in state law that lets undercover officers have sex with prostitutes during investigations, but they won’t say how often — or even if — they use the provision.

The idea has shocked advocates and law enforcement experts in the sex trade, who note that many prostitutes have been forced into that line of work.

“I don’t know of any state or federal law that allows any law enforcement officer undercover to … do what this law is allowing,” said Roger Young, a retired special agent who for more than 20 years worked sex crimes for the FBI from Las Vegas and who has trained vice squads around the country. “Once we agree on the price and the sex act, that’s all that you need. That breaks the law.”

Honolulu police say they need the legal protection to catch lawbreakers in the act. Otherwise, they argue, prostitutes will insist on sex to identify undercover officers.

This year legislators moved to revamp Hawaii’s decades-old law against prostitution. They toughened penalties on pimps and those who use prostitutes. They also proposed scrapping the sex exemption for officers on duty. The legislation was amended to restore that protection after police testimony. The revised proposal passed the state House and will go before a Senate committee Friday.

Selling sex would remain a petty misdemeanor under the proposal.

During recent testimony, Honolulu police said the sex exemption protects investigations and should remain in place.

“The procedures and conduct of the undercover officers are regulated by department rules, which by nature have to be confidential,” Honolulu Police Major Jerry Inouye told the House Judiciary Committee. “Because if prostitution suspects, pimps and other people are privy to that information, they’re going to know exactly how far the undercover officer can and cannot go.”

They also assured lawmakers that internal policies and procedures are in place to prevent officers from taking advantage of it. The Honolulu police vice officers who investigate prostitution haven’t been accused of sexual wrongdoing in recent memory, spokeswoman Michelle Yu said in an email, but added that in 2011 a parole officer was fired after being charged and convicted of sexual assault against a prostitute.

Advocates warn that the provision is an invitation for misconduct.

“Police abuse is part of the life of prostitution,” said Melissa Farley, the executive director of the San Francisco-based group Prostitution Research and Education. Farley said that in places without such police protections “women who have escaped prostitution” commonly report being coerced into giving police sexual favors to keep from being arrested.

“It doesn’t help your case, and at worst you further traumatize someone,” said Derek Marsh, who trains California police in best practices on human trafficking cases and twice has testified to Congress about the issue. “And do you think he or she is going to trust a cop again?”

Charlie Fuller, executive director of the International Association of Undercover Officers, laughed when he heard about the Hawaii law. Contrary to Hollywood movies that portray undercover officers having to break the law to blend in with bad guys, Fuller said good investigators always have other options.

“A good undercover,” he said, “is going to get probable cause before they have to cross that line.”