Tánaiste Leo Varadkar says Fine Gael has removed the party whip from three of its members, who attended an Oireachtas Golf Society event in Galway on Wednesday night.
Mr Varadkar said the event "should not have happened."
In a statement, he said: "I understand how extremely difficult the restrictions have been for people and the enormous sacrifices we have all made.
"Funerals, christenings, weddings, family holidays and other really important family occasions have been foregone to protect each other and the most vulnerable.
"As representatives we should lead by example.
"In recognition of the seriousness of this matter, I have removed the party whip from Senators Jerry Buttimer, Paddy Burke and John Cummins."
Senator Jerry Buttimer has also resigned his position as Leas-Chathaoirleach of the Seanad.
Mr Varadkar added: "All have apologised profusely and accept they made a serious error of judgment."
Meanwhile the EU Commissioner for Trade Phil Hogan, who also attended the event, said the the Irish Hotels’ Federation assured them that arrangements in place would meet Government guidelines.
He said: "I attended the Oireachtas Golf Society dinner on Wednesday on the clear understanding that the organisers and the hotel concerned had been assured [by the Irish Hotels’ Federation] that the arrangements put in place would be in compliance with the government’s guidelines.
"Prior to the event, I had complied fully with the Government's quarantine requirements, having been in Ireland since late July."