The seat has becoming increasingly marginal due to major demographic change from its working class past to sought after inner city living.

Mr Danby's current margin is 3.6 per cent and Labor strategists have the seat, which includes St Kilda, Balaclava and South Melbourne, on a watch list of seats potentially under threat, with a major change in demographics in Albert Park and Port Melbourne favouring the Liberals.

Mr Danby has held Melbourne Ports since 1998 but requires preference flows to defeat the Liberals, who last election won the primary vote.

At the 2013 election Mr Danby won 31.6 per cent of the primary vote, behind Liberal candidate Kevin Ekendahl​ who won 41 per cent - the Greens picked up 20 per cent of the primary vote.

In 2010 Mr Danby won 38.2 per cent of the primary, to the Liberals 37.8 per cent. Three years earlier Mr Danby won 42.5 per cent to the Liberals 39.7 per cent.

Mr Danby recently made public comments saying that he would put the Liberals ahead of the Greens in preferences, after a mooted preference deal between the Greens and the Liberals in some Labor held seats including Wills and Batman surfaced.

In retaliation Labor is threatening to dampen the Greens chances in the Liberal seat of Higgins by running an open ticket – Labor preferences would be essential to any Green hope of unseating frontbencher Kelly O'Dwyer.

Labor party officials say the MP will not be setting the preferences and that discussions with other parties had yet to begin.

This fact has not deterred the Greens, who have seized on Mr Danby's comments to campaign against him as a conservative.

The Greens commissioned a ReachTEL poll of more than 800 voters last Wednesday night in the seat to determine if they supported Mr Danby's position to preference the Liberal party ahead of the Greens. It also asked if this would change how they voted.

On the question of whether voters supported the move, 45 per cent backed it, but critically 60 per cent of Labor voters opposed the move.

Asked if the policy would change how they voted, 48 per cent of Labor voters said they would be less likely to vote for Mr Danby – overall 36 per cent of voters in the electorate said they were less likely to back the incumbent.

For Mr Danby's preferences to be distributed the Greens would have to leapfrog Labor into the second position.

Mr Danby said Labor's preferences had never been distributed in Melbourne Ports and described his position as symbolic.

Mr Danby said he understood a deal between the Liberals and Greens had already been done.

Greens MP Adam Bandt said the poll showed Labor voters were "rightly appalled" at Mr Danby's policy.

"In the three horse race in Melbourne Ports, I expect progressive Labor voters will shift to the Greens' Steph Hodgins-May rather than risk their preferences electing the Liberals," Mr Bandt said.  

The Greens are on the attack in Melbourne Ports, angry with Labor MP Michael Danby for saying he wants to preference the Liberals ahead of the Greens. Photo: Andrew Meares

The Liberal candidate for the seat is Owen Guest.

ALP assistant state secretary Kosmos Samaras said preferences would be determined by the party.

"We are yet to sit down with the Greens or any other party to discuss preferences, I anticipate that will happen closer to the election,'; he said.