Liberal MP Ann Sudmalis is expected to announce she will not to recontest the next election, dealing Prime Minister Scott Morrison another damaging blow.
Mr Morrison tried to persuade the marginal seat-holder not to quit politics, but Ms Sudmalis has reportedly knocked back his entreaties and decided to bow out.
She holds the southern NSW coastal seat of Gilmore with a margin of just 0.7 per cent and has faced a preselection challenge from local real estate agent Grant Schultz.
Cabinet minister Christopher Pyne argued being elected to parliament was not a "life sentence".
"It's not compulsory when you get elected to remain in parliament for the rest of your life," Mr Pyne told reporters in Canberra on Monday.
"Most people get defeated by their preselectors, or they get defeated by the electorate, so if you get to retire it's not a bad way to go. If Ann Sudmalis has decided to retire, I wish her the best of luck."
Labor MP Stephen Jones, whose seat of Whitlam borders the Gilmore electorate, said Ms Sudmalis had given in to factional infighting.
Cabinet Minister Christopher Pyne has defended the Liberal Party's preselection process. Source: AAP
"Ms Sudmalis has been caught up in Liberal factional warfare on the South Coast. To her credit she has been batting on, but it now appears that her heart is no longer in it," Mr Jones tweeted on Monday.
The MP's possible exit comes as the Liberal Party faces a backlash over its lack of commitment to preselecting women.
Mr Morrison backed a female candidate to run in the seat of Wentworth, vacated by former prime minister Malcolm Turnbull, but the preselection was won by former diplomat Dave Sharma.
AAP understands only six women have been preselected for safe Liberal seats across the country.
Fighting for her political future earlier this year, Ms Sudmalis said the government was doing a "damn good" job and there was no reason to knock her off.
"We've got a great horse - the government's doing a phenomenal job - so why flick the jockey off? That's my words to my preselectors."
Mr Morrison stood beside Ms Sudmalis to offer his full support.
"Ann has demonstrated that she is the right candidate here, because she has won this seat in tough contests," he said at the time.
"If it wasn't for Ann at the last election, Bill Shorten would now be prime minister."
