Days after the nations' major newspapers blacked out their front pages to protect press freedom, Labor's attorney-general spokesman Mark Dreyfus urged the federal government to rule out the prosecution of Dan Oakes, Sam Clark and Annika Smethurst for publishing classified documents.

The letter, also signed by home affairs spokeswoman Kristina Keneally and communications spokeswoman Michelle Rowland, urged the government to fully comply with its obligations under freedom of information laws and better protect whistleblowers.

"Labor believes a strong and independent media is vital to holding governments - and opposition parties - to account," the letter reads.

"All Australians, as well as friends in democracies around the world, were shocked earlier this year to see Australian Federal Police raiding the offices of media organisations and the home of a respected political journalist.

"The Prime Minister dismissed widespread public concerns about these raids with a wave of the hand and a glib one-liner saying 'it never troubles me that our laws are being upheld'.

"What we are seeing with this third-term Liberal government is an ever-growing culture of cover-up and denial.

"Scott Morrison and his senior ministers treat press freedom as if it were an inconvenience rather than as an essential pillar of our democracy."