The front pages of newspapers such as The Sydney Morning Herald, The Australian, Financial Review, The Daily Telegraph, among others, were printed with large sections appearing to have been censored with black ink, bearing a red seal with "secret, not to be disclosed" written on it, Efe news reported.

"The culture of secrecy that has descended through these legal provisions restricts every Australian's right to know and goes well beyond the original intent of national security," Media Entertainment and Arts Alliance union head Paul Murphy said in a statement.

The actions by the print media come in the footsteps of a television campaign launched on Sunday night, led by Australia's 'Right to Know' group, of which the broadcasters ABC and SBS, and Channel 9 are a part.

"When the government hides the truth from you, what are they covering up?" read ads rolled out on the country's media networks.

The campaign comes after the police raided ABC's Sydney headquarters in June and the residence of a News Corp journalist in Canberra for allegedly leaking secret documents.

Two ABC journalists and the News Corp reporter face a possible prison sentence for the alleged leaks, although Attorney General Christian Porter announced in late September that any legal proceedings against a journalist must first be authorized by his office.

Since 2001, Australia has passed 75 laws to strengthen national security. The latest among them, adopted last year, extended prison sentences for disclosing classified information.

Murphy said it was time to knock down these excessive laws and decriminalize journalism and informants, as it served the public interest.