Prominent Turkish journalists Can Dundar and Erdem Gul, from the newspaper Cumhuriyet, are due to go on trial charged with revealing state secrets.
They were arrested in November 2015 over a report alleging that the Turkish government had tried to ship arms to Islamists in Syria.
Can Dundar and Erdem Gul deny the charges but face possible life sentences if found guilty.
Supporters of the two journalists say the case is an important test of press freedom in Turkey.
The Turkish government has come under increasing international criticism over its treatment of journalists.
Earlier this month, Turkish police raided the offices of the country’s biggest newspaper, Zaman, hours after a court ruling placed it under state control.
Can Dundar, Cumhuriyet‘s editor-in-chief, and Erdem Gul, Ankara bureau chief, were arrested in November 2015.
President Recep Tayyip Erdogan personally filed a criminal complaint against the Cumhuriyet journalists.
They were held on pre-trial detention but were released in February after the Constitutional Court ruled their rights to liberty and free expression had been violated.
Can Dundar said the government was trying to intimidate Turkey’s journalists.
“There’s an effort to arrest an entire profession and the public – what foreigners call a <<chilling effect>>,” he said.
“What’s trying to be created is a mechanism of self-censorship and an increasing empire of fear.”
Campaigners say the case is politically motivated and part of a growing crackdown on media critical of President Recep Tayyip Erdogan.
On March 24, dozens of prominent writers published an open letter to PM Ahmet Davutoglu, urging the government to drop the charges against the Cumhuriyet journalists.
“We believe that Can Dundar and Erdem Gul are facing life in prison simply for carrying out their legitimate work as journalists,” they said.
The letter also voiced concern over the “increasing climate of fear and censorship and the stifling of critical voices in Turkey”.
Zaman newspaper is closely linked to the Hizmet movement of influential US-based cleric Fethullah Gulen.
The government says Hizmet is a “terrorist” group aiming to overthrow Recep Tayyip Erdogan.
Fethullah Gulen was once an ally of Recep Tayyip Erdogan but is now seen by the Turkish President as a threat to his authority.