Journalists took out a protest march in Kathmandu on Monday
Many newspapers in Nepal have appeared with a blank space instead of an editorial to protest against attacks by Maoist activists.
Dozens of former rebels attacked staff and vandalised offices at Himal Media, one of the country's biggest newspaper publishing houses, over the weekend.
The protesters said the Nepali Times and other magazines carried articles critical of the communist party.
Nepal's Maoist Prime Minister Prachanda has denied any role in the attack.
He told Nepal media the attack was by "immoral agents" who had "infiltrated" the Maoists.
The UN and US have both criticised the violence, in which journalists were assaulted.
In a joint statement, Nepali media organisations condemned the attacks and said they would escalate their protest until the ruling Maoist party stopped the violation of press freedom.
"This is the first in a series of escalating protests that our media companies will launch if the current organised attacks on us by groups affiliated to the ruling party are not stopped immediately," the Media Society and Editors' Alliance in Nepal said in a statement.
Prachanda pledged an investigation into the incident
The prime minister said he had ordered an investigation into the attack.
The New York-based Committee to Protect Journalists called for an independent and non-partisan investigation into the attack.
On Sunday, dozens of former rebels attacked Himal Media and demanded the reinstatement of Maoist-affiliated employees who had been sacked recently.
Some reports said they were also angry at coverage critical of the Maoists.
Himal Media said the attack had nothing to do with labour relations but was an effort by the Maoists to control the media.
"This is a direct attack on free press and democracy," said Kunda Dixit, editor of the Nepali Times, which is published by Himal Media.
Quoted in Nepal media, Prachanda said there would be an investigation into the incident and action taken against the perpetrators.
"There are people who in the guise of the Maoists are engaged in giving a bad name to the party," Prachanda was quoted as saying.
"Our party is constantly struggling to rid the party of these elements."
Hundreds of journalists marched through the capital, Kathmandu, on Monday in protest at the attack.
The Maoists became the largest parliamentary party in April's elections after ending a decade-long civil war.