Sue Gilroy, the president of the Singleton Business Chamber, was announced on Monday as the party's candidate for the May 22 Upper Hunter race.

"Our community needs leaders not pretenders. Unfortunately, we've been a safe seat for too long and that means we've been taken for granted," Ms Gilroy said in a statement.

"I'm a businesswomen, a registered nurse, I've worked in mining and I grew up on a farm. I've never lived in a city in my life. I dare say few people would be able to say that in NSW Parliament."

SFF party leader Robert Borsak introduced Ms Gilroy, saying she was "very much on the page with the party" on coal mining, which is looming as a significant election issue.

Ms Gilroy said she wanted to keep coal and agriculture jobs in the Hunter and make sure those sectors were sustainable.

Asked how to make mining more sustainable environmentally, she she said she did not have an answer to that yet.

"Clean energy needs to still be on the table," she said. "Coal won't be here forever but it's going to be here for a long time yet."

Mr Borsak accused the government of trying to shut down the coal industry. He singled out Premier Gladys Berejiklian for criticism on that front, describing her as "about as popular up here as a pork pie in a synagogue".

The by-election was sparked by Nationals MP Michael Johnsen's resignation on March 31 after he was accused of raping a woman in 2019, which he denies.

Ms Gilroy is so far the only woman candidate in the race. She said on Monday gender shouldn't make a difference.

The May 22 poll is expected to be tight despite the Nationals and its predecessor party holding the electorate for nearly a century.

The seat was whittled away to a 2.6 per cent margin in 2019, when Mr Johnsen scooped up 34 per cent of first preferences.

Labor trailed on 28.6 per cent and the Shooters, Fishers and Farmers Party candidate on 22 per cent.

One Nation will also contest the by-election.

Ms Berejiklian will head to the Upper Hunter this week to campaign alongside the Nationals candidate, David Layzell.

If the government loses the seat it will have the difficult task of governing in minority status until the next election which is due in March 2023.

Labor is expected to announce its candidate on Tuesday.

Australian Associated Press