It comes after allegations of "disgusting behaviour" towards an 18-year-old led to Mr Costigan's suspension, revealed on Wednesday night.

A second complaint, by a 20-year-old woman about an alleged incident when she was 19, came shortly after the first complaint and was forwarded to the LNP's disputes committee for investigation.

The state executive's decision to expel Mr Costigan was unanimous.

Mr Costigan was given the opportunity to provide a right of reply but declined and did not attend the meeting on Friday in Brisbane.

LNP leader Deb Frecklington called on Mr Costigan to resign his seat rather than join the crossbench in Parliament.

"I do not believe Mr Costigan deserves to represent the people of Whitsunday," she said.

"He has disgraced the office and he should go now."

Ms Frecklington said if her office or the LNP received any more complaints about Mr Costigan they would be referred to Speaker Curtis Pitt and, if necessary, the police.

Mr Costigan has vowed to remain in Parliament and has strenuously denied the allegations. Attempts were made to reach Mr Costigan for comment.

LNP acting president David Hutchinson said the party fully recognised the significance of expelling Mr Costigan and understood that removing a sitting MP would make the challenge of winning the next state election more difficult.

“However, we expect our elected representatives to meet the highest standards,” he said.

“Our priority will always be ensuring that we have the right people representing the LNP in Parliament, regardless of the political cost.”

The incident involving the first woman arose after the 18-year-old arrived at her grandparents' home and found Mr Costigan alone and shirtless.

Mr Costigan had arranged to stay at the home while on holidays in Victoria and was unaware the teenager was due to arrive.

He admitted he took selfies with the teenager but claimed she was as "happy as Larry".

However, Brisbane Times understands the woman told her mother she was holding a duress alarm in her handbag.

The mother alleged Mr Costigan's behaviour was "extraordinary".

"It was predatory, sexual, unhinged and intimidating," she said in an email to the LNP.

"My daughter was terrified the entire time she was there.

"She is traumatised by his revoltingness."

Earlier, Mr Costigan described the allegations as "baseless" and said he would pursue defamation action.

"I'm not going to roll over on this," he said.

"It is a stitch-up."

Mr Costigan said the 18-year-old did not look intimidated or concerned, showing the media selfie photos he took with her.

Ms Frecklington said she was horrified to see Mr Costigan display the selfies during his press conference.

"I want to thank those media organisations who chose not to publish the photo of that young girl," she said.

Ms Frecklington said the 18-year-old was vulnerable and only two months out of high school.

"Unwanted publicity stops victims of harassment from coming forward," she said.

Mr Costigan was previously branded a "sleazebag" by Deputy Premier Jackie Trad after he posted a video of himself on a beach with two tourists wearing bikinis on World Bikini Day in 2017, which he described as "political correctness on steroids".

However, asked whether Mr Costigan - who describes himself as a "bikini fan" on his Instagram account - should have been reprimanded earlier, Ms Frecklington was defensive.

"The Whitsundays is a holiday destination, there are many people in bikinis there, however, I have very high standards for my team, Mr Costigan doesn't meet those standards," she said.

"As soon as I had the complaint, I directed that to the LNP, the LNP acted immediately."