The New South Wales Nationals have not ruled out expelling an MP if he takes on the upper house president role offered by his long-term friend, Labor's Premier Chris Minns.
Ben Franklin, who is godfather to one of Mr Minns's children, has been asked to consider the prestigious job, which comes with a pay rise and a government car.
It would also mean the Coalition would lose a crucial vote in the Upper House, stifling its ability to vote against government legislation.
Nationals leader Paul Toole said he had asked his colleague not to accept.
"I've indicated to him that there could be consequences, and that would be a matter for the party room and central executive," Mr Toole said.
"As part of the coalition agreement, no Liberal or National party member of the upper house is to stand for the president or the vice-president position."
He said Mr Franklin had told him he had not yet made a decision, but losing a member's voting power would be a blow to the opposition in an already tight legislative council.
"We know how critical every vote is going to be in the upper house and that is why we need every set of hands on the floor to be able to support the opposition to hold the government to account," he said.
The Federal Member for Riverina Michael McCormack said Mr Franklin should remember who got him elected.
"I'd say to Ben Franklin just remember those people who supported you to get you where you are," Mr McCormack said.
"Once things don't go your way or you get a better offer to do something in the political sphere you've got to remember the people who put on the yellow T-shirts.
"Remember those people and remember the people you represent, don't throw your toys out of the cot and stick true to what you said all along when you first stood for the election."
Mr Minns and Mr Franklin met as members of Young Liberals and Young Labor and, despite some political differences, forged a cross-party friendship.
On Wednesday, Mr Minns said his government would be open to a non-government member serving as president of the legislative council.
He said it "could be the case" the move would make it easier to pass legislation.
"It is a recognition that we do not have the numbers," he said.
The premier said he had spoken to Mr Franklin and asked if he would support his friend for the job. Mr Minns said he would.
The ABC has contacted Mr Franklin for comment.
