The NSW government says it will consider any plan to stop unlicensed brothels taking advantage of laws that allow them keep operating illegally.

Premier Morris Iemma has encouraged Sydney's north shore councils, which are battling to close unlicensed brothels offering unprotected sex, to seek legislative changes from the government.

"The enforcement of this area of the law is with councils," Mr Iemma said. "If the Local Government Association or the councils have got a proposition they wish to put to the government that would ease their burden on cracking down on the illegal activity then I'm happy to consider that," Mr Iemma said.

At least three brothels have been operating illegally in Roseville for nearly two years, Ku-ring-gai Council officials say.

The council has spent thousands of dollars trying to shut down the brothels but has failed. Private investigators hired to obtain evidence acceptable to a court have successfully solicited unprotected sex in at least one of the brothels.

But when the NSW Health Department approached the brothel proprietor they denied the claims and said they only offered massage services, which they are licensed for.

Therefore, the council must take action against suspected illegal brothels in the Land and Environment Court. The council has said previously the legal process is long and potentially unsuccessful because the suspected brothel owners may shut down and move on before they must appear in court.

Other north shore councils including Willoughby and Lane Cove have reported to be experiencing similar problems. Nine councils across Sydney have paid private detectives $25,000 to have sex with prostitutes to gather sufficient evidence against illegal brothels, News Limited reported today.

AAP