Labour Party MEP Proinsias De Rossa was assaulted outside Liberty Hall last night following a public meeting on the Lisbon Reform Treaty.
Mr De Rossa was verbally abused and knocked to the ground.
He suffered minor cuts during the incident, which is being investigated by gardaí.
A statement by Labour leader Eamon Gilmore said that Mr De Rossa was very shaken by the incident.
Mr Gilmore condemned the assault and ‘anti-democratic tactics’, saying he was greatly shocked by what had happened.
He said that when Mr De Rossa left the meeting, he was confronted by a group of men, some of whom had been present at the meeting and had spoken aggressively against the Treaty.
Labour is backing the Lisbon Treaty and Mr De Rossa had been attending the meeting to discuss the issues surrounding it.
A Government spokesman has condemned the reported assault on the 67-year-old MEP.
The meeting on Monday night was one of a series that the party has planned to inform the public of the provisions of the Treaty and to put Labour's case for a 'yes' vote in the June referendum.
The anti-Lisbon Treaty group Libertas has 'utterly condemned' what it called a 'disgraceful attack' on Mr de Rossa.
A spokesperson for the group said that while they completely rejected Mr de Rossa's views on the Lisbon Treaty, he has a right to articulate those views without having fear for his safety.
They added that no member of Libertas was at the meeting after which the attack happened, and hoped that the Labour MEP has a quick recovery.
