HONOLULU, HAWAII—Honolulu police officers have urged lawmakers to keep an exemption in state law that allows undercover officers to have sex with prostitutes during investigations, touching off a heated debate.

Authorities say they need the legal protection to catch lawbreakers in the act. Critics, including human trafficking experts and other police, say it’s unnecessary and could further victimize sex workers, many of whom have been forced into the trade.

Police haven’t said how often — or even if — they use the provision. And when they asked legislators to preserve it, they made assurances that internal policies and procedures are in place to prevent officers from taking advantage of it.

But expert Derek Marsh says the exemption is “antiquated at best” and that police can easily do without it.

More: Why Honolulu Police Want to Be Allowed to Have Sex With Prostitutes