Several people sustained minor injuries this morning at the UCD campus at Belfield when gardaí and protesters clashed at a picket line.
Violent clashes developed after dozens of gardaí moved on around 70 picketers who were stopping vehicles entering a building site on the campus.
A garda suffered a head injury and minor concussion after falling during the scuffles. A number of protesters also sustained minor injuries, as did a photographer with the Evening Heraldwho reportedly was hit by a car and struck by a garda.
The picketers were protesting against Collen Construction Ltd, who successfully sought a committal order against three bricklayers who picketed one of their sites in Ballybrack.
The High Court jailed the men two weeks ago for failing to give an undertaking not to picket the site where Collen are building social housing for Dun Laoghaire/Rathdown County Council.
The men claimed they were refused jobs at the site because they were active members of the Bricklayers and Allied Trades Union (Batu).
Since they were jailed, there have been a number of protests in support of them at Collen site in Dublin and several hundred people marched through the city centre.
Richard Boyd Barrett, a spokesman for the "Ballybrack Three" was at the protest today and condemned the Garda tactics.
"Though many of the gardai have expressed sympathy with our protest, others are being extremely heavy handed," Mr Boyd Barrett said. "A small number of guards took the opportunity to lash out at protesters with punches."
He also questioned why there has been such a large police presence at the pickets which were placed on the site last week. He said between 30 and 50 officers have been on duty at the picket this morning.
Collen has been targetted because it subcontracts work to firms which refuse to employ union labour, according to the protesters.
"It's a disgrace that the resources of the state, and taxpayers' money, can be used so swiftly and unquestioningly in support of a wealthy developer while working people who stand up for a fair wage and decent working conditions can be thrown behind bars," Mr Boyd Barrett said.
There have been scuffles at the site since the picket began last week. Some workers on the site have refused to cross the picket line but others have forced their way through in vehicles, on some occasions knocking picketers down.
Mr Boyd Barrett said the protests would continue until the three men were released from jail and Collen entered into negotiations on the terms of employment for workers on its sites.
Collen has complained that its workers have been intimidated at the protests in Ballybrack, where the site is now temporarily shut, and at the Hugh Lane Municipal Gallery in Dublin city centre where another protest is taking place.