Peter Costello has stepped down as chairman of Nine Entertainment with immediate effect, following allegations of an altercation with a News Corp journalist at Canberra airport. In a statement on Sunday evening, Costello expressed gratitude for the board’s support but emphasized the need for new leadership to guide the company forward.

Costello, who also resigned from his directorial role at Nine, was accused last week of pushing Australian newspaper journalist Liam Mendes. Mendes claimed he was pushed by Costello while asking about Nine’s response to allegations of sexual harassment and bullying within the company. Costello refuted the accusation, stating that Mendes had fallen over an advertising placard.

Costello stated that he had planned to retire after the July Olympics and before the annual general meeting in November but decided to advance his departure. He expressed support for Nine’s CEO, Mike Sneesby, and the company’s investigation into historical complaints of harassment.

The media union MEAA criticized Nine for its slow response to concerns raised by staff about management’s failure to ensure safe workplaces. Michelle Rae, the union’s acting director, said the appointment of a new chair was an opportunity to address these issues and improve management culture.

This leadership change at Nine follows the abrupt departure of former news and current affairs director Darren Wick, after allegations of sexual harassment and inappropriate behaviour. Sneesby has faced scrutiny over his knowledge of these allegations and the terms of Wick’s departure, which reportedly included a substantial payout.

The incident reportedly took place at Canberra airport on Thursday when Mendes approached Costello with questions. A Nine spokesperson defended Costello, stating that the journalist collided with a placard while walking backward and filming, and that Costello did not strike Mendes.

No formal reports have been filed with ACT policing regarding the incident, a spokesperson confirmed on Sunday evening.

Catherine West, the former deputy chair, has been appointed as the new chair of Nine Entertainment. The board expressed gratitude to Costello for his decade-long contribution, highlighting his role in significant milestones such as Nine’s re-listing on the Australian Stock Exchange in 2013, the News Media Bargaining Code, and the merger with Fairfax Media.