Egyptian Journalists Syndicate president Yahiya Kallash, secretary general Gamal Abd el-Rahim and freedoms committee chief Khaled Elbalshy have been charged with aiding fugitives after two reporters sought by police staged a sit-in at the union's offices.
Their arrest following a May 1 police raid on the union building to detain two reporters from an opposition website accused of inciting demonstrations drew condemnation from rights groups.
Saturday's hearing lasted just a few minutes and the trial was adjourned to June 18 at the request of defence lawyers who asked for more time to review the case, an AFP reporter and one of the lawyers said.
The three are currently free on bail.
"This trial is a new attack against public freedoms," Elbalshy told AFP.
"We should not let this pass," he added.
His lawyer Ahmed Abdelnaby said the defence team asked for an adjournment in order to review the prosecution file against their clients.
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"The accusations are not serious and there is no evidence" against them, Abdelnaby said.
He said the trio risk a two-year jail sentence if convicted of harbouring fugitives and on charges of "publishing false news".
Around 50 supporters demonstrated outside the court brandishing pens and signs that read: "Journalism is not a crime," the AFP reporter said.
Earlier this week, the European Union said the indictment of the journalists' syndicate members was "a worrying development".
"It reflects broader limitations on freedom of expression and press freedom in Egypt," an EU spokesperson said in a statement.
Rights activists accuse President Abdel Fattah al-Sisi of running an ultra-authoritarian regime that has violently suppressed all opposition since toppling Islamist president Mohamed Morsi in 2013.
Kallash had denounced the police raid on union headquarters to arrest reporters Amr Badr and Mahmud al-Sakka, saying the government was "escalating the war against journalism and journalists".
Amnesty International has called the latest crackdown on journalists "the most brazen attack on the media the country witnessed in decades."