Around 200 non-commissioned officers had been granted permission to protest at a Police Club in Cairo, where they called on officials to come to discuss their pay demand with them.
When they received no response they marched to the Interior Ministry in defiance of the new law. Security sources said they shoved barricades at fellow members of the security forces outside the club, before the protesters were allowed to march.
Seperately, police fired tear gas to disperse supporters of ousted Islamist President Mohamed Morsi who gathered in front of al-Azhar University in Cairo and at Mansoura University, north of Cairo on Sunday.
Unrest has helped topple two Egyptian presidents in less than three years. Veteran autocrat Hosni Mubarak was ousted after a popular uprising in 2011, while the army removed Morsi on July 3 following mass protests against his one-year rule.
Police have arrested thousands of Morsi's Islamist supporters who have been staging rallies calling for his reinstatement, and the army-backed interim government passed the new protest law to strictly regulate public gatherings.
Security forces have fired tear gas and water cannon to disperse protesters who defied the protest law in recent weeks.
On Thursday Egyptian authorities ordered three prominent activists to stand trial on protest-related charges. One of them, leading dissident Ahmed Maher, was charged with protesting without permission.