Fiji's Women's Crisis Centre says most women turn to prostitution out of poverty and new powers in the crimes decree will make matters worse.
Prostitution has always been illegal in Fiji, but only the sex workers were held accountable in the past.
The decree has expanded the powers to also cover the client and prosecute all those involved in making money from the transactions.
The interim government says the changes are needed to modernise Fiji's laws and there have been police raids.
The organisation's coordinator, Shamima Ali, believes the measures won't help.
"Nowhere in the world where prostitution has been criminalised in this manner has prostitution gone away. I believe that we'd be better served if we address the issue of gender inequalities, looked at women's education, looked at women's economic empowerment. I believe those are things that will help get rid of prostitution."
The powers will also target women 'loitering' in the streets at night and Shamima Ali says it could invite abuse of power.