The chief executive of media company Nine has acknowledged "serious" claims of "alleged inappropriate behaviour" at the network, and announced a review of its "concentration of power".

In an internal email to all staff obtained by the ABC, chief executive Mike Sneesby said he was meeting with Nine News staff on Monday afternoon to discuss what he called "broader cultural issues".

"Recent reports that detail alleged serious failings of leadership in television news clearly tells me more works needs to be done to ensure we have a safe and inclusive workplace throughout Nine," Mr Sneesby wrote.

Mr Sneesby also denied having ever asked staff to sign non-disclosure agreements after making a complaint.

"At Nine, I have never signed NDAs for any employee relating to a complaint or behavioural issue," he said.

The email goes on to announce an external firm will conduct an independent review of the "behaviours and concentration of power that has damaged the trust and fairness within our television newsrooms".

Staff are encouraged to report issues via an external complaint line, or to Nine's executive group, the email said.

"We will provide a helpline for emotional or psychological support that is private and independent," it said.