Turmoil is continuing within the Labour Party as it heads toward Sunday's contentious candidate selection in Manurewa with current MP George Hawkins threatening to resign and force a byelection if the party selects a candidate he dislikes.

The party will select its new candidate to replace the retiring George Hawkins on Sunday and Mr Hawkins is understood to have told Labour leader Phil Goff he would force a byelection or publicly criticise the party if candidate Jerome Mika was selected.

Mr Mika is an Engineering Printing and Manufacturing Union official - and Mr Hawkins is understood to have a dislike of the union and its influence over the party.

Labour's affiliated unions are also battling as they line up behind their preferred candidates - split between expected frontrunners Mr Mika and Louisa Wall.

Asked if he was concerned about Mr Hawkins' threat, Labour president Andrew Little said it would be "unfortunate" if Mr Hawkins felt the need to quit this close to a general election.

"I think everybody's preference would be that he stays, but we can't control this and he left himself open the option to do that a couple of months ago."

Mr Hawkins had indicated he could leave when he was elected to the community board in local body elections earlier this year.

Mr Little said as national secretary of the EPMU he would stand aside from his Labour president's place on the selection panel because he was Mr Mika's employer and northern representative Robert Gallagher would take his place.

The candidate selection will potentially put the 600 local members and Labour's affiliate unions head to head with the national council representatives and EPMU.

While the EPMU supports Mr Mika, the Service Workers Union, the Maritime Union and Amalgamated Workers Union support Louisa Wall. If the two sides can not agree on either candidate, they could choose a third person as a compromise rather than take a majority vote. The other contenders are MP Ashraf Choudhary, Ian Dunwoodie, Amelia Schaaf, Shane Te Pou and Raj Thandi.

Service Workers Union head Jill Ovens said the union had rung its 600 members in the electorate to urge them to vote. Ms Wall and her parents had links to the union and she believed it was also time the Labour Party had a woman MP in a South Auckland based seat. However, she said Mr Hawkins' threat to stand down was "unhelpful".

The three unions are also supporting List MP Phil Twyford in Te Atatu, which will have its selection a week later. Mr Twyford's chances could be hurt if Mr Mika is selected for Manurewa because of calls for more female candidates in Auckland. Mr Little rejected arguments that the outcome of the Manurewa selection will affect the Te Atatu selection a week later.

Yesterday former MP Dover Samuels also criticised the union influence in the Manurewa selection, saying it was unjust that union representatives were included on selection panels for general seats but Maori representatives were not. He said the party should include one of its Maori national council members on the selection panel on Saturday, given there were two Maori candidates standing - Shane Te Pou and Louisa Wall.