WA Nationals MP Louise Kingston has accused Opposition Leader Shane Love of bullying and harassment as she announced her resignation from the party.
Ms Kingston made the allegation during a tearful address to the state's Legislative Council on Thursday afternoon.
"It gives me no pleasure to have to say what I am going to have to say today," she said.
"Unfortunately, I've been the victim of relentless bullying and harassment by the leader of the Nationals."
Ms Kingston said she had raised the issue with others and Mr Love directly and did not make a formal complaint with the party because she "believed the situation had been resolved".
"I believed everyone had learnt from the situation and used the opportunity to grow and build better relationships," she said.
"Unfortunately, I have now learnt a hard lesson."
Mr Love on Thursday afternoon confirmed Ms Kingston's resignation from the party.
"While it is disappointing Ms Kingston no longer wishes to be part of our Nationals WA team, we thank Ms Kingston for her service to our party," he said in a statement.
The member for Western Australia's southwest told the chamber she had been "punished by an underhanded campaign" during preselection earlier in June, "and the party decided I was not worthy to be a part of their team going forward by preselecting me in an unwinnable position".
"I hope by me speaking out, others will learn from my experience and find the courage to speak out also," Ms Kingston said.
She said the situation was "a pattern of behaviour".
"People come and go, but in more recent times many talented people have left and I now join those people," Ms Kingston said.
"I sincerely hope that this leads to further changes in the party to address the issues I have raised."
Nationals WA president Julie Freeman said the party had a robust harassment complaints policy and the state director had confirmed that no complaints had been lodged regarding the issue raised by Ms Kingston.
"We acknowledge that Louise was disappointed with the outcome of the preselection process," Ms Freeman said in a statement.
"There was a large number of quality candidates seeking winnable positions on the ticket.
"The candidates are selected by delegates who are democratically elected by our grassroots membership."
Ms Kingston took over the southwest seat in September 2023 after Nationals-turned-independent James Hayward was booted from WA's parliament.
Hayward resigned from the WA Nationals after being charged in 2021 with child sexual abuse but continued to sit in the state's upper house as an independent MP.
Hayward is serving a prison term of two years and nine months after being convicted in October 2023.
In November 2023, more turbulence hit the party, with Nationals MP Merome Beard swapping camps to join the Liberals.
Afterward, Mr Love suggested the party could be persuaded to surrender the Opposition leadership to the Liberals.
