About a dozen women were arrested over the weekend in a Honolulu prostitution sting.

But instead of being arrested on suspicion of prostitution, they face sex assault charges.

If convicted, the women would have to register as sex offenders and could spend up to a year in jail. A prostitution charge carries just 30 days.

Legal experts say the new tactic from the Honolulu police department is extremely unusual.

Honolulu police spokeswoman Michelle Yu said she was checking to see if the department would comment on the allegations.

Hawaii has a strange history with prostitution investigations. Until a year ago, police officers were legally allowed to have sex with prostitutes. State lawmakers changed that policy last year after The Associated Press highlighted the loophole.