Dáil Eireann has passed a motion calling for a tribunal of inquiry into the murders of RUC superintendents Harry Breen and Robert Buchanan.
The two men were shot dead in 1989 by the Provisional IRA as they returned from a meeting with gardaí in Dundalk.
The tribunal will examine claims of Garda collusion with the killers.
The officers were ambushed shortly after they crossed the border. Minister for Justice Michael Dowell challenged Sinn Féin TDs to say that republicans would cooperate with the inquiry.