It is also certain to deepen the rift between Egypt's liberal and secular pro-democracy campaigners many of whom participated in the 2011 popular uprising against Hosni Mubarak and the current military-backed government.
The ongoing campaign against dissent and pro-democracy activists has been overshadowed by a much larger crackdown against the Muslim Brotherhood group and other Islamists. That push has led to the death of hundreds and the jailing of at least 16,000 people since the July ouster of President Mohammed Morsi.
The wife of Ahmed Douma, one of the three activists, wrote on her Twitter account that she was headed there. Douma suffers from stomach ulcer and has complained in past court hearings that he was not being properly treated in jail.
The three activists Ahmed Maher, Mohammed Adel and Douma were leading figures in Egypt's 2011 popular uprising that toppled long-time autocrat Mubarak.
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The three were accused of violating a controversial new law on holding street protests and were sentenced each to three years in prison in December.
The court also ruled today that each of the three would be fined USD 7,140.
"The judge, regretfully, has upheld the sentence on Douma, Maher and Adel. Down, down with the oppressive verdict," one of their lawyers, Gamal Eid, wrote on his Twitter account, minutes after the ruling was read by presiding Judge Ahmed Faisal.
Another defence lawyer, Ahmed Seif al-Islam, said he planned to challenge the ruling, but acknowledged that the process could take months.