Leader of Egypt's 6 April movement jailed for protests
Amr Ali was also ordered to pay a fine of 500 Egyptian Pounds ($63).
Three others defendants in the same case received a similar sentence, though in absentia.
"This is a political ruling," 6 April spokesperson Sherif al-Ruby told The New Arab on Tuesday.
"Egypt's judiciary does not base its rulings on the law. Instead, it follows direct orders from the authorities," he explained.
Ruby added that the movement's members would meet on Tuesday night to decide on the action to be taken against the "illegal" ruling.
Ali, the opposition movement's general coordinator, was arrested from his home in the Menoufiya governorate last September.
However, there was no official acknowledgement of his arrest for the first few days, leading many to consider it a case of forced disappearance.
The youth movement leader was later located at Tora prison after being interrogated without the presence of a lawyer.
Ali succeeded Ahmed Maher in his post. Maher is currently serving a three-year prison sentence for allegedly breaking the protest law, which critics say sought to criminalise dissent.
Prior to his arrest, the new 6 April general coordinator had sought to establish an umbrella formation for revolutionary forces against the current regime.
|Egypt's judiciary does not base its rulings on the law. Instead, it follows direct orders from the authorities.
- Sherif al-Ruby
Ali also sought to launch a campaign to work for the release of the scores of activists and prisoners of conscience detained by the regime of Abdel Fattah al-Sisi.
In December, the movement announced that two of its members, Mohammed Nabil and Ayman Abdel Magid, had been kidnapped from their homes by unknown assailants.
The group held the Egyptian authorities and security services fully responsible for the safety of the two men, who are members of the movement's political bureau.
The 6 April movement oroginally grew from a campaign for labour rights in the textile factories in al-Mahalla al-Kubra. Workers had organised a strike on 6 April 2008, to protest against poor wages, poor management and unfair practices.
Forced disappearances have been of particular concern in Egypt, as Cairo officials have been accused of causing hundreds of people to "vanish", according to local and international human rights organisations.
In June 2015, Human Rights Watch issued a report highlighting the issue of enforced disappearances in Egypt, calling on the authorities to "immediately disclose" the whereabouts of the forcibly disappeared and to "hold those responsible to account".
"The authorities should either release anyone illegally detained or charge the person with a recognisable crime," the report added.