Fairfax announced on Tuesday it would cut five per cent of its full-time workers - 550 staff - across Australia and New Zealand, prompting a mass walkout at its offices including in Melbourne and Sydney.

Almost one third of the positions to go are journalists.

Carlton, a prominent media identity, was fired after refusing to cross the picket line to write his weekly column for the Herald's Saturday edition.

"I can confirm that Mike Carlton's agreement as a contributor to Saturday's Sydney Morning Herald has been terminated after he refused to file as normal his column for Saturday's morning paper," a Fairfax spokeswoman said today.

The radio broadcaster's hosting job on the breakfast show on 2UE, also owned by Fairfax, has not been affected, management said.

"It's my understanding that Mike was unprepared to write during the strike," 2UE's general manager Simon Rufus said.

"It's got (nothing) to do with the radio station. He'll be back on Monday."

The journalists' union said the sacking was a demonstration of what was wrong with Fairfax management.

"This is an indication again that the new regime at Fairfax Media is embarking on a low quality approach to journalism," a spokesman for the Media Entertainment and Arts Alliance said.

"The management prepared to trample on anyone who gets in their way and the people who will lose out in this case are the Sydney Morning Herald readers."

Fairfax staff in Sydney and Melbourne went on strike yesterday until Monday over the company's job cut plans.

The MEAA said the Workplace Ombudsman was investigating potential unlawful actions from Fairfax over Carlton's sacking.