Mr Frank McBrearty Snr has said he is prepared to go to jail and on hunger strike rather than appear as a witness at the Morris tribunal.
The tribunal was sitting in Dublin this morning to hear applications for legal representations in the inquiry into alleged Garda corruption in Donegal.
"We'll definitely not going to be there," Mr McBrearty said after this morning's hearing in Dublin. "The Government are telling lies."
When asked if he was aware of the consequences of refusing to appear he said: "I'm prepared to go to jail and to go on hunger strike."
He also insisted that no member of his immediate family nor the extended McBrearty family would appear, whether they were called or not.
Mr McBrearty had earlier asked Mr Justice Morris to apply to the Dáil to have the terms of reference of the Inquiry expanded. "We are the ones that suffered, but we won't be able to participate under the current terms of reference."
He said he wanted the role of the Minister of Justice, the Attorney General, the Garda Commissioner and the State solicitor in Donegal investigated.
However, Mr Justice Morris refused, saying the Dáil had already agreed on the scope of the tribunal and to seek to alter this would be undemocratic.
He assured Mr McBrearty, however, that his request for funding for legal representation would be granted and that witness expenses would be paid.
Fine Gael said this afternoon that it would press in the Senate for an extension of terms of reference for the tribunal, as requested by Mr McBrearty.
Senator Jim Higgins said the McBrearty family would not appear unless this extension was granted. "The absence of the McBrearty family from the Tribunal would render the proceedings meaningless," he said.
