Rebel Wilson’s lawyers say they will appeal a California court’s decision that cleared the way for the Australian actor to be sued for defamation, in a claim that could run into millions of dollars.

On Sunday, Wilson’s attorney Bryan Freedman said in a statement that an immediate appeal would be lodged against a Los Angeles superior court decision that was handed down on Saturday morning AEDT.

The court threw out Wilson’s claims that under California’s anti-Slapp laws, the accusations she made against the producers of her directorial debut film The Deb constituted “protected activity”.

Her lawyers had argued that the allegations, made in July on Wilson’s Instagram account which has more than 11 million followers, were a matter of public interest. They said the court should strike out the defamation suit filed by her producers, who were using the legal system to silence the Australian.

However, Judge Thomas Long ruled that Wilson’s public statements had not been made as a matter of public interest. Long said they were made “in the context of Wilson’s private business dispute with [the] plaintiffs surrounding the production and premiere of the film”.

The judge also noted that despite some of Wilson’s accusations against her producers being of a criminal nature, she had not sought any criminal prosecution. Instead, the dispute appeared to centre around a letter of demand the actor sent to the producers, seeking additional payments, a record deal, and a writing credit.

On Sunday, Freedman said the court’s ruling defied well-established law.

“Posting a video addressing the highly anticipated premiere of The Deb at the Toronto international film festival and widespread misconduct in the entertainment industry, which are unmistakably ‘matters of public interest’, constitutes a protected activity,” he said.

“Similarly, a demand letter addressing the same and related topics that was allegedly distributed after litigation has started is also protected activity. A notice of appeal will be filed today. We are more than confident that the court of appeals will rule in our favour.”

Lawyers acting for The Deb’s producers, Amanda Ghost, Gregor Cameron and Vince Holden, who had been accused by Wilson of, among other things, sexual misconduct, embezzlement and unlawful detainment, said they were gratified by the latest court ruling, which would allow them to proceed with the defamation case.

Camille Vasquez, the attorney who successfully defended Johnny Depp in the defamation case against his ex-wife Amber Heard, said Wilson’s anti-Slapp motion had been “a cynical attempt to stifle a valid legal claim after she launched a public attack against three hardworking professionals”.

“We look forward to seeing Ms. Wilson in court,” Vasquez said in a statement.

Wilson launched her anti-Slapp motion after the producers sought a 90-day stay in the Los Angeles superior court in October, to establish the source of an anonymous website called amandaghostsucks.com, in which allegations similar to the ones Wilson made on Instagram were posted.

In statements filed in the court, Vasquez stated that shortly after the producers initiated the defamation action against Wilson, she sent them a series of emails threatening to “very publicly ruin them”, including one on 29 July warning she was poised for “going public”.

Two days later the anonymous amandaghostsucks website was registered, Vasquez alleges, where “grotesque lies” were made, including allegations that Ghost, who is of Indo-Trinidadian heritage, was an “Indian Ghislaine Maxwell”.

The website has since been pulled down due to legal reasons.

Earlier this month, The Deb lead actor Charlotte MacInnes, who had been at the centre of the sexual misconduct accusations Wilson has made against Ghost and her husband, filed a declaration in the court saying she had become “deeply disturbed” by Wilson’s behaviour on set and her allegations against the film’s producers were “completely false and absurd”.

MacInnes’s declaration said she had felt bullied harassed by the director and had “no idea what could cause Wilson and her attorney to make up such lies about me.”