The accusations comes from women who worked on his gardening show Burke's Backyard in the 1980s and 1990s, after a joint investigation by Fairfax/ABC.
He has been labelled a "psychotic bully", a "misogynist" and a "sexual predator" by female employees.
The 70-year-old denied all allegations in a statement on Sunday.
"The bitter irony is that I have had a life-long opposition to sexism and misogyny," he said. "Burke's Backyard was a lone bastion of anti-misogyny from its inception in 1987."