Egypt's Journalists' Syndicate condemned a wave of arrests ahead of protests planned for Monday against the handover of two strategic Red Sea islands to Saudi Arabia.
"The nation as a whole will pay the price for the return of the security state and the unleashing of [security] agencies to deal with those holding differing views," the syndicate said Saturday.
Rights lawyers said that dozens of people were arrested in round-ups in cafes in central Cairo and other cities on Thursday night as well as raids on homes.
April 15 saw the largest non-Islamist protests against President Abdel-Fattah al-Sissi's government in two years, amid public anger over the plan to hand over the islands of Tiran and Sanafir to Saudi Arabia.
The handover was quietly announced during a visit to Cairo by Saudi King Salman and provoked outrage on social media and among the Egyptian opposition.
Protests without prior police approval have been effectively banned under a law passed months after al-Sissi, then head of the armed forces, ousted Islamist president Mohammed Morsi in mid-2013.
Lawyer Ragia Omran, of the Front for the Defence of Egypt's Protesters, said that a fellow lawyer in her group had been detained by prosecutors for 15 days.
Haitham Mohammedein, who is also a well-known leftist activist, was accused of belonging to Morsi's banned Muslim Brotherhood, calling for protests, and conspiring to overthrow the government, Omran said.
A total of about 75 people appeared to have been arrested in the sweep, which was "obviously an organized campaign," she said, but lawyers had not yet been informed of the potential charges against the remainder.
Lawyer Mokhtar Mounir of the Association for the Freedom of Thought and Expression put the overall number arrested at more than 100.
The Journalists' Syndicate said the houses of two journalists had been raided.