Finance Minister Vic Fedeli has served former PC Leader Patrick Brown with a letter of intent saying he'll sue.
Brown recently released a book detailing what he calls a political takedown of his career.
It includes a damning allegation against Fedeli.
Brown claims a female staffer left him a note accusing Fedeli of sexually inappropriate behaviour back in December 2017.
Fedeli has categorically denied the allegations calling them false and without merit.
In the letter served to Brown and his publisher, Fedeli and his lawyers are demanding an apology and that the accusations be retracted from the book.