Minor scuffles broke out at a demonstration at the gates of the Dail as politicians returned for their first day after the summer break.
A group of about 150 gathered opposite Leinster House on the edge of Kildare Street to protest against Fine Gael and Labour policies.
Metal barricades had been erected on Molesworth Street and around the Dail, which were manned by uniformed gardai.
After scuffles broke out involving a small number of protesters, gardai drew batons and used pepper spray.
The protest groups included Claiming Our Future, a non-party-political network of activists, which had rallied anti-austerity protesters to urge the Government to tax the rich in the forthcoming budget.
"As gardai ran to detain the people who were heading towards the gates of the Dail, dozens surged forward and pushed the barrier forward," one eye-witness said.
"There was then some scuffling, and protesters and gardai were knocked to the ground."
An elderly man was treated for a minor injury to his head, while a woman was seen having some of her clothes pulled from her back amid the struggle.
The garda dog unit and mounted officers were called in as reinforcements, along with an ambulance to treat any wounded.