Journalists at Fairfax Media, one of Australia's largest publishers, have gone on strike after the company announced plans to cut 120 jobs.

Staff were informed of the proposed redundancies and reduced editorial budgets via email on Thursday.

The cuts are expected to affect journalists at the Sydney Morning Herald, The Age and the Australian Financial Review.

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 took to social media to express their disappointment, saying they wouldn't return to the office until Monday.

"No auction results, no Grand Prix coverage nothing until Monday," Fairfax digital editor Saint Bhakthi tweeted.

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.

Australia's media sector is grappling with falling print advertising revenues.

Fairfax's Sydney Morning Herald is one of the country's most-visited news websites, but competition in the digital news space is fierce.

The Huffington Post, The Guardian and the Daily Mail have all created large Australian newsrooms to compete with Fairfax and News Corp Australia titles.