The New York lawyer and former Noraid leader, Mr Martin Galvin, said he has been threatened by men who claimed to represent the Provisional IRA.
Mr Galvin, who opposes the Belfast Agreement, said the threats were made on Saturday in a pub in New York where he had organised a function for the Republican Prisoners Welfare Fund, which supports the families of Real IRA prisoners.
Mr Galvin said two men, approached him. "One of the men said he represented the Provisional IRA. He said he knew where I lived and it would be easy to run me down with a car."