Garish signs over Bangkok's girlie bars and massage parlours openly advertise an industry comprising an estimated 3 per cent of Thailand's economy.

But prostitution is technically illegal, pays no taxes, fosters police corruption and treats its workers like slaves.

Clearly, the government says, it's time to open a debate on legalising and regulating the sex business.

The Justice Ministry will hold an unprecedented public discussion of its proposal to legalise prostitution and register sex workers.

"We (will) tackle this problem one way or another," Justice Minister Pongthep Thepkanchana said in a recent interview. "Maybe we will approach the problem of prostitution differently than we do now."