NSW Premier Dominic Perrottet's brother says a parliamentary inquiry is nothing more than "ill-informed, speculative and defamatory commentary", as the NSW Liberals scramble to fill a vacancy ahead of the state election.
It comes after Mr Perrottet rebuffed questions over his brothers' whereabouts last week, telling media to "Leave my family out of it".
The premier's brother Charles Perrottet wrote a defiant letter to a NSW upper house committee, after they requested he attend a hearing over allegations of impropriety in the Hills Shire Council.
"I will not be participating in your Labor/Greens circus," Charles wrote to the committee, the The Daily Telegraph reports.
"I reserve my position in relation to the partisan, ill-informed, speculative and defamatory commentary."
The inquiry was launched after Liberal MP Ray Williams used parliamentary privilege to allege several senior party members had been paid to install councillors onto the Hills Shire council, to be friendly to developer Jean Nassif.
The inquiry was told last week another Perrottet brother, 26-year-old Jean-Claude Perrottet, joined with Hills Shire councillor Chistian Ellis to offer businessman Frits Mare $50,000 to stack the seat of federal Liberal MP Alex Hawke and remove him from parliament.
The committee has since engaged professionals to serve a summons on Jean-Claude and Mr Ellis, however Charles cannot be summonsed to the inquiry as he not a resident of NSW.
The committee had received the letter, inquiry chair and Greens MP Sue Higginson told AAP.
"(Charles) Perrottet is entitled to hold and express his opinions to the media about the parliamentary inquiry and the MPs on the committee," Ms Higginson said.
"However, once again, as chair of the committee, I encourage him to attend the hearing of the committee and express his views and provide evidence to the committee on the substantive matters the committee has been asked to inquire about."
The inquiry addressed important issues in the public interest, she said.
"There (have) been serious allegations by a Liberal member of parliament," committee member and Labor MP Penny Sharpe told AAP.
"I urge him (Charles) to change his mind and to co-operate with the inquiry."
The premier has previously dismissed the inquiry as a political hit job being run by NSW Labor in the lead up to the state election.
"The Labor Party are playing smear games with my family," Mr Perrottet said last week.
Meanwhile, the NSW Liberal Party is scrambling to fill a suddenly vacant spot on their upper house election ticket, weeks out from the ballot.
Prospective candidates are jostling for the position on the party's upper house ticket, after MP Peter Poulos was expelled from the party at the weekend over an explicit photo scandal.
Outgoing transport minister David Elliott has asked Mr Perrottet to be considered for the No.2 spot on the ticket, which would secure him another eight years in parliament.
However, Mr Perrottet did not endorse Mr Elliott on Monday, saying the matter would ultimately be up to the party.
As the state edges towards the March 25 election, Labor leader Chris Minns said the government was "focused on themselves" and mudslinging.
"I think for many voters, they'd see that as a preview of the next four years if the coalition is re-elected," he told reporters.
