News Corp journalist Annika Smethurst's High Court challenge against secrecy laws looms as a significant and unprecedented test of the constitution's protections for democratic freedoms, according to constitutional law experts.

The first hearings in Smethurst's case will take place in Canberra on Tuesday and Wednesday, five months after the journalist's home was raided by police as part of a leak investigation. Smethurst's lawyers are challenging the criminal law used to justify the search warrant, arguing it is unconstitutional overreach.

News Corp journalist Annika Smethurst's case looms as a major constitutional test. Credit:Dominic Lorrimer

In April 2018, Smethurst revealed an internal proposal to expand the domestic role of electronic intelligence agency the Australian Signals Directorate. The story was based on leaked documents and the police search warrant cited the section of the Crimes Act that prohibits unauthorised release of official secrets.

Smethurst's legal team contend that, while there is a legitimate need for some level of secrecy, the current law allowed for the illegitimate purpose of protecting governments from embarrassment and "government secrecy as an end in itself".