Author Clementine Ford has resigned from her long-running column for Nine's newspaper arm, criticising the publisher and saying she was disciplined over a tweet calling Prime Minister Scott Morrison a "f***ing disgrace".

In a series of posts on Twitter, Ford said she was threatened with termination in September 2018, when the newspapers were still under the banner of former publisher Fairfax Media.

"They said that [the] new policy was we 'didn't disrespect the office of the PM'," Ford said.

Ford said she had made the comment about the Prime Minister following his tweet last year about "gender whisperers" in schools, which referenced a News Corp article about teachers reportedly being trained to identify transgender students.

On Wednesday, Ford accused her former publisher of bowing to pressure from rival media companies and protecting the Prime Minister.

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"Clementine Ford has been a contributor for The Herald and The Age for the past seven years and we thank her for her work over that time," Monique Farmer, life editor of The Sydney Morning Herald and The Age, said in a statement provided by a Nine spokesperson.

The spokesperson declined to comment on the existence of a policy regarding the Prime Minister's office.

Fairfax Media's social media policy, which covered contributors, prohibited the use of "abusive language".

Ford, who has been contacted for comment, has courted controversy before over things she has said on social media.

Last year, Lifeline cancelled an event featuring Ford after an online petition drew attention to tweets of hers with the phrase "all men must die".