Dozens of women held a vigil Sunday outside Egypt's presidential palace, challenging a law that restricts protests and calling for the release of thousands of prisoners detained for violating the controversial measure.

Organizers said they didn't seek prior permission from authorities to stage the vigil near the palace of President Abdel-Fattah el-Sissi.

Police formed a cordon around the women, who raised photos of detainees. Some protesters raised banners that read: "Ramadan is not the same without you," in reference to the Muslim holy month of fasting that brings families together.

The protest law, in place since 2013, criminalizes any gathering of more than five people without prior police permission and imposes hefty fines and prison sentences on violators. Authorities say the law is necessary to end the chaos that plagued Egypt since its 2011 revolt.

Activists say the law is used to muzzle critics. Thousands of people have been detained over the law, with some sentenced to as many as 15 years for protesting and allegedly using violence.

Prominent women rights defender Yara Sallam and activist Sanaa Seif, who hails from a well-known family of rights defenders, were arrested a year ago Sunday outside the palace for opposing the law and are currently serving two-year sentences along with 21 other activists.

Some in the protest Sunday posted on their Twitter accounts that journalists were harassed, with one of them saying that his pictures of the protest were deleted by police. There were no reported arrests.