DUBLIN (AFP) -- Amnesty International was going through a fraught vote Tuesday on whether the human rights organisation should back decriminalising prostitution, following a heated debate on the divisive issue.

Some 400 delegates from 70 countries have gathered in Dublin and will vote on the draft policy. If it passes, it will help form Amnesty's policy on the global sex trade.

"We want to see a legal framework in place whereby all elements of sex work are decriminalised," Thomas Schultz-Jagow, Amnesty's senior director of campaigns and communications, told AFP.

He said there was "evidence that criminalisation of consensual adult sex work can lead to increased human rights violations against sex workers."

But controversially, the document proposes decriminalising third parties involved in prostitution, such as brothel operators, alongside sex workers.

In response, the Coalition Against Trafficking in Women (CATW) penned an open letter saying Amnesty's name would be "severely tarnished" if it approved the policy, which it said sides with "exploiters rather than the exploited".

"There's no logic behind the premise that in order to protect those who are exploited you have to decriminalise the exploiter. It makes no sense," CATW executive director Taina Bien Aime told AFP.

"It is really important for Amnesty to understand the world is watching and they would really lose a tremendous amount of credibility as a human rights organisation if this is supported."

The group cites a 2012 study which found a rise in reported human trafficking to countries where prostitution was legalised, though accompanied by improvement in working conditions for sex workers.

The letter was signed by more than 600 women's rights groups, sex trade survivors and actors including Oscar winners Meryl Streep and Kate Winslet.

More than 8,500 people have added their signatures to the petition online.

Opponents of the draft policy stress it fails to recognise the many reasons -- including poverty, violence and coercion -- that draw people into prostitution.

"The demand for commercial sex is what fuels trafficking. You cannot then turn around and say let's protect those who are promoting the demand," said Esohe Aghatise, anti-trafficking manager with women's rights group Equality Now.

Schultz-Jagow admits it is a "complex and divisive issue" but argues that the London-based organisation is used to debating complex and emotive topics such as abortion and the death penalty.

"The importance of the issue for us is that there's a particular marginalised and vulnerable group that will benefit from a decriminalisation approach," he said.

Amnesty stress that the proposals do not change its long-standing position that forced labour and trafficking for the purposes of sexual exploitation constitute serious human rights abuses and must be criminalised.

The varying legislation in different countries reveals the depth of division on the issue in Europe alone.

France recently moved to criminalise the buying rather than selling of sex -- known as the "Nordic model" and already adopted in Iceland, Sweden and Norway.

Prostitution by force is banned all over Europe, but legislation differs between countries. Sex work is legal and regulated in Austria, Germany, the Netherlands, Switzerland and elsewhere.

The vote follows a two-year consultation of research from United Nations agencies, academics, non-governmental organisations and human rights lawyers.

The vote was expected to take place after 1100 GMT, with the result due to be announced within hours.