Member for the state's southwest, Louise Kingston, accused Shane Love of "relentless bullying and harassment" during an address to the state's Legislative Council on Thursday afternoon.
Mr Love says he doesn't know what he allegedly did to Ms Kingston and that he had tried to contact her but received no response.
"I think that this is the result of a difficult and bruising pre-selection process," he told ABC News on Friday.
"We have a small party but we're a party that actually cares about people."
During her address, Ms Kingston said she had raised the issue with Mr Love and others but did not make a formal complaint because she believed the situation had been resolved.
She also 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".
Federal Nationals leader David Littleproud said there were formal processes that should be followed if Ms Kingston was unhappy with the party's pre-selection decisions.
"That is something that should be looked at ... whether that be internal National Party processes or through the Western Australian parliament," he told ABC.
"I'll respect the processes. I think you've got to be very careful to delve into something that could go to a formal process."
Minister for Planning and Homelessness John Carey said it had been "incredibly brave" of Ms Kingston to speak about her experience.
"A member is crying in parliament and resigns from the party. I mean, it's deeply concerning," he said.
"Shane has questions to answer and so I do think that there appears to be a toxic culture in the National Party. And that's why we're seeing so many people either resign or stand down. It's deeply concerning
Nationals WA president Julie Freeman previously 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.
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.
After being convicted in October 2023, he is serving a prison term of two years and nine months.
In November 2023, more turbulence hit the party with Nationals MP Merome Beard swapping camps to join the Liberals.
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