El-Dostour newspaper journalists sitting in at the paper headquarters came under attack by unidentified men Saturday night.
The sit-in has been staged for eight days now.
The attackers threw stones and empty soda bottles at the windows of the headquarters and smashed the building's glass door and fled the scene.
The protesters rushed to Dokki police station to report the incident and an investigation has been opened.
The journalists, who asserted that their sit-in is peaceful and that their demands are legitimate, said they received threats to end their protest.