One of Australia's largest publishers Fairfax media will cut the equivalent of 120 full-time jobs, report said.

The cost-cutting measures are expected to affect journalists at The Sydney Morning Herald, The Age and Australian Financial Review.

Staff were informed of the proposed redundancies and reduced editorial budgets via an email, which was released by media website Mumbrella.

The media union described the cuts as "savage" and a "body blow".

"It's the staff on the newsroom floor who have driven the transition to digital and through all the challenges continued to produce high quality independent journalism. And this is the reward... We will be fighting for every job," said Paul Murphy, chief executive of the Media, Entertainment and Arts Alliance.

Staff at The Sydney Morning Herald and The Age in Melbourne have held stop work meetings.

The email from Fairfax editorial director Sean Alymer said the decision to cut jobs was based on "our understanding of our audience".

"Change is a permanent part of our industry. It is a reflection of what we know about the ways our readers are consuming our stories. We must continue to evolve with them," Mr Alymer said.

A Fairfax article published online on Thursday afternoon said the media sector is grappling with falling print advertising revenues.

Some staff took to social media to express their disappointment: "120 jobs to go across Melbourne and Sydney newsrooms at Fairfax. I honestly don't know what is going to be left. Devastating," Sunday Age writer Jill Stark tweeted.