Labour MEP Prionsias De Rossa was allegedly beaten up after a public meeting to discuss the Lisbon Treaty in Dublin last night.
Mr De Rossa (67) was involved in a fracas with a group of up to five people outside Liberty Hall after the meeting to discuss the upcoming referendum.
It is understood the group included opponents of the Lisbon treaty who tackled Mr De Rossa and followed on the street before the incident. Some of the group had been inside the meeting, which had been organised by the Labour party.
Mr De Rossa was badly shaken and receieved minor cuts to his hand. He spoke to gardai after the incident.
A Garda spokesman said: "We are investigating an incident involving an assault outside Liberty Hall last night." The spokesman refused to give further detail on the incident.
Labour Party leader Eamon Gilmore condemned what he called "anti-democratic tactics" employed by the group who are opposed to the Lisbon Treaty.
Mr Gilmore said that when Mr De Rossa left the meeting at about 10.30pm he was confronted by a group of men, some of whom were at the meeting.
“One of the group shouted abuse at him through a loud-hailer,” Mr Gilmore said in a statement released this afternoon.
“When he objected to being filmed by one of the group with a camcorder he was knocked to the ground and some of those involved sat on his back pinning him to the ground.
“The Gardai arrived and took statements from those involved. Proinsias suffered minor abrasions and is quite shaken by the assault. “
“The Labour Party wants to have a serious debate about the Lisbon Reform Treaty. We are more than happy to engage in calm and rational debate with opponents of the Treaty.
Mr Gilmore said the “anti-democratic tactics” demonstrated last night “must not become a feature of this referendum campaign”
Speaking on RTÉ’s Liveline radio programme this afternoon, party colleague Joe Costello said Mr De Rossa was badly shaken by the assault.
“He was certainly very put out. I never saw him in such bad form that he was really hurt by it all,” Mr Costello said.
“He was bleeding from his hand. He had been assaulted and he had been set upon.
“He was very badly shaken up. It was the first time in his political career he had been assaulted.”