CAIRO - Three of the most prominent secular activists involved in Egypt's 2011 revolution were convicted Sunday of holding a rally without authorization and attacking police officers, receiving three-year prison terms and hefty fines in the first use of a controversial new law.

Judge Amir Assem found Ahmed Maher, Ahmed Douma and Mohammed Adel, founders of the April 6 youth movement, guilty of violating the law passed last month. Each of them also faces fines of $7,250.

April 6 helped organize the demonstrations that toppled longtime authoritarian leader Hosni Mubarak in 2011 and, like many other liberal activists, supported this year's campaign for elected Islamist President Mohammed Morsi to leave office.

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Since Morsi was toppled by the military on July 3 after millions-strong demonstrations, however, the movement claims there has been a return of Mubarak-era police brutality and the curtailment of the freedom of expression - notably the protest law.

The government has described the law as an attempt to bring order and stability to the streets amid continued protests by Morsi's supporters, hundreds of whom have been killed and thousands jailed. But rights groups and politicians warn the new law is an attempt by the military-backed government to curtail dissent, particularly ahead of planned elections that would pave the way for an elected post-Morsi leadership.

A referendum on the constitution amended after Morsi's ouster is planned for Jan. 14-Jan. 15.

The court gave in its verdict one of the first legal defenses of the new law. It comes after lawyers filed a constitutional challenge to the statute during the trial.

"The law was not drafted to deprive the people of their right to organize public meetings, and peaceful protests. It was drafted to organize this right" in accordance with the constitution currently in place, according to details of the ruling published on the state news agency.

Defense lawyer Alaa Abdel-Tawab said he will appeal the court decision, describing it as "exceptionally harsh" for a misdemeanor court. "This is a court verdict with a political flavor," he said, adding that the first use of the law came less than a month after it was passed.

"We have long asked for speedy trials against officials from the Mubarak regime. They have answered our demands but are trying us, and fast, instead," Abdel-Tawab said.

Egypt's state news agency said the ruling also included putting the three under surveillance for three years after they serve their term -- an unusual decision, particularly against political activists.

The agency said the defendants broke out in chants of "Police are thugs" and "Down, down with military rule" after the verdict. They had already been in detention and will now begin serving their sentences.

New York-based Human Rights Watch said the new law empowers security agencies intent on "crushing the right of Egyptians to protest the actions of their government." They say authorities are now also targeting secular activists, like the three sentenced Sunday, who have criticized the successive leaderships that have ruled Egypt since Mubarak's 2011 ouster.

Heba Morayef, Egypt Director for Human Rights Watch, said the case against the three, a similar referral of 24 other protesters and a leading blogger in Cairo to trial and others in the country's second city Alexandria, appears to be the beginning of a new trend of targeting high profile activists who were behind the Jan. 25, 2011, protests.

The protesters had used rampant police abuse as a rallying cry against Mubarak and his nearly 30 years in power.

"I see this as very much as the beginning of a serious crackdown on the Jan. 25 generation of protesters. They are the ones who the Interior Ministry sees as disruptive and the ones to blame for its own loss of status," Morayef said. "Not only is it a trend, but it is also a reflection of the new empowerment" of the police force, which had rallied strongly for the new law.

She called the implementation of the law an "overreach on the part of the Interior Ministry" which wants to restore its image and practices to the pre-2011 uprising period. "But it forgot that (these) led to 2011."

But with authorities showing growing signs of intolerance for criticism, and a largely pro-military media, the activists are increasingly finding little few forums to mobilize pro-democracy campaigns, said Moreyaf. "That is what is ultimately empowering" to the police, she said.

Authorities have also found support from a large segment of the public that has grown wary of protests.

The three activists were charged with holding an illegal protest and assaulting policemen after Maher turned himself in for questioning because he was wanted for holding an earlier protest. A crowd of supporters gathered outside the courtroom where Maher was Nov. 30, leading to scuffles with the police officers who later fired tear gas.