It's a testament to Joel Fitzgibbon's legacy that two of the rival candidates who may vie to succeed him were in unison in their praise for the outgoing MP. 

Mr Fitzgibbon's decision not to contest the next federal election will end a term that began in 1996, but his hold on the coal mining electorate has slipped amid divisions within Labor over the impacts of its climate policies.

Those tensions were on display in a bruising 2019 election campaign in which Mr Fitzgibbon sustained a 14.2 per cent hit to his primary vote.

One of his main challengers, One Nation candidate and Singleton coal miner Stuart Bonds, picked up 21 per cent.

Mr Bonds fell out with the party but said he was "checking the field out" ahead of deciding whether to now run as an independent.

"The last thee years he's done a great job, been a great advocate for the coal mining industry in this area.

"It's unfortunate that the rest of the Labor Party haven't listened to Joel, haven't heeded his warning, and I think they're set up to make the same mistake they made going into the last election."

Questioned on whether it would be his responsibility to plan for a transition away from coal if he was elected, Mr Bonds was unequivocal.

"I don't think it is the job of the politicians anywhere, it's up to the free market," he said.

'What the ALP should be'

Deputy Prime Minister and Nationals leader Barnaby Joyce told the ABC his party would be targeting Hunter at the next election.

James Thomson, 29, who works as a community relations officer at a local school, was pre-selected as the Nationals candidate in May.

He described his own approach to climate and energy policy as "outcome-focused".

"Climate change is one of those issues which looks to divide people, and as somebody with a young family and young children, I want to get away from that division."

He would not be drawn on whether he would support a target of net zero emissions by 2050.

"I support each and every family and worker in my electorate," Mr Thomson said.

"We have to get away from some of these buzzwords like 'transition' and focus on diversifying our economy."

From safe to marginal seat

Until the last election Hunter was considered a safe Labor seat, but Mr Fitzgibbon saw his two-party-preferred margin shrink from 12.5 per cent to 3 per cent.

His primary vote fell 14.2 per cent to 37.6 per cent but remained ahead of the Nationals (23.5), One Nation (21.6), the Greens (6.9) and United Australia (4.3).

The electorate includes the towns of Cessnock, Singleton and Muswellbrook as well as urban areas on the western shore of Lake Macquarie.

ABC's chief elections analyst Antony Green says Hunter's economic base is a peculiar mix of agriculture and heavy industry, being dominated by coal mining and electricity generation, but also possessing some of the country's best vineyards, horse studs and richest cattle-grazing areas. 

Tensions within Labor over its climate policies and approach to coal, encapsulated by Mr Fitzgibbon's decision to quit the shadow ministry in November last year, make it entirely feasible that the party can lose the seat it has held since 1910. 

If Hunter does fall, it makes it harder for Labor to pick up the net seven seats (notionally after redistribution) it needs to have a majority in the House of Representatives.

Win back coal votes: Fitzgibbon

Mr Fitzgibbon offered registered nurse Emily Suvaal and Olympic shooter and former miner Dan Repacholi as possible successors.

Peter Jordan, the president of the CFMEU's mining division, has backed Mr Repacholi.

Also in the mix is union official and former coal miner Jeff Drayton, who Mr Fitzgibbon described as a "great candidate" in the Upper Hunter state by-election.

Labor will be desperate to avoid a repeat of that result, which saw a 7.5 per cent swing away from the party. 

"The Upper Hunter by-election did concern me," Mr Fitzgibbon told the ABC after making his announcement.

"Because I was typically experiencing people walking past me saying: 'G'day Fitzy, how are you going? You're doing a good job but what's wrong with your party?'

One Nation has announced former coal miner, Singleton businessman Dale McNamara as its candidate.

Mr McNamara contested the Upper Hunter by-election for the party.