Detained members of a hardcore Zamalek football club fan group started a hunger strike on Saturday, their official Facebook page reported.
At least 36 members of Ultras White Knights are detained pending investigations for violating the protest law, which activists deem too restrictive and have launched a wide hunger-strike campaign against it.
"White Knights detainees begin a hunger strike in the prisons of darkness," the announcement said on the Facebook page without giving further details.
The 36 members were arrested after reportedly being involved in clashes with security forces in Cairo's Shubra neighbourhood. The fans were protesting against the detention of some of their colleagues who are accused of trying to assassinate club chairman Mortada Mansour last August.
Following the alleged attempt, Zamalek club management decided to distance itself from the group.
Several other members of Ultras White Knights were arrested in subsequent demonstrations.
The Ultras White Knights detainees are joining 66 other prisoners that have already started a hunger-strike in Egyptians jails. Many others, including families, journalists and political parties joined a hunger strike in solidarity with them.
They demand the release of all detainees in what they described as cases of freedom of opinion.
They also call for amending the protest law that bans demonstrations without prior authorisation and gives security the right to bar any gathering of more than ten people. Hundreds have been arrested under this law.