The NSW Labor Party conference has passed a motion to stop giving automatic preferences to the Greens.

Labor and the Greens have been involved in a war of words in recent weeks, and the Greens say the stoush will only bolster support for the Opposition.

The rift widened in Sydney on Saturday, with fierce debate about how Labor should best distance itself from the Greens.

NSW Labor secretary Sam Dastyari, who has led recent attacks against the Greens, urged his party to take the Greens on in an attempt to increase Labor's primary vote.

Mr Dastyari told delegates Labor must redefine its relationship with the Greens.

"The free ride is over," he said.

Government whip Joel Fitzgibbon says the Greens have become a real political threat to Labor, without being held accountable for their more radical policies.

"This motion sends a very clear message to them," he said.

"In the future when deliberating over these preference deals we will be taking into account what they do and how they behave - delegates it's very, very important."

'Ideas and principles'

Before the motion was passed, the left faction slammed the right for making the issue about preferencing.

Federal Government frontbencher Anthony Albanese says there are better ways to make voters see the difference between Labor and the Greens.

"Labor will defeat the Greens political party by the value of ideas and principles," he said.

Left faction stalwarts like veteran Senator John Faulkner argued the party's public focus on backroom preference deals woul do nothing to draw back voters from the Greens.

"You have to win votes to get preferences to give," he said.

But in the end a clear majority of delegates from both factions voted in favour of the motion.

Gillard pressured

The move comes after Victorian Labor decided to preference Family First ahead of the Greens in a state by-election for the seat of Melbourne.

Prime Minister Julia Gillard owes her minority Government in part to an alliance with the Greens, who helped give her the numbers to take power after the 2010 election.

However, Labor's relationship with the Greens has proven to be somewhat of a poisoned chalice for the Prime Minister, whose negotiations with the Greens included having to back-flip on her promise not to introduce the hugely controversial carbon tax.

The Greens' Sarah Hanson-Young says Labor needs to sort itself out, and stop blaming others.

"To me it looks like the Labor party attacking themselves all over again, cannibalising their own vote and devouring their own values," she said.

"This is more about an attack on themselves than attack on the Greens."

The Opposition wants Ms Gillard to say whether she backs the resolution when she appears at the conference on Sunday.