Fine Gael is to oppose the Government amendment to the motion before the Dail on the Iraqi crisis.
Foreign Affairs spokesman Gay Mitchell says it is "unacceptable" for TDs to approve action which does not have UN backing.
According to Fine Gael the Government amendment is a complete reversal of previously stated policy, namely that it supported multi-lateral UN sanctioned action only.
The Government's amendment now states that it is giving a commitment in the event of military action being sanctioned against Iraq, either with or without further US sanction, to review the situation regarding overflight and landing facilities to initiate a debate in the Dail.
Mr Mitchell says it is completely unacceptable that the Government to ask the Dail to approve action which the UN does not sanction.
Fine Gael wants the Minister for Foreign Affairs to explain why the Government has now changed its policy in this area.
The Taoiseach says the current build-up of military in the Gulf is not an act of war.
Bertie Ahern quoted UN Secretary General Kofi Annan saying the build up is happening primarily to force Saddam Hussein to face up to his responsibilities.
"Kofi Annan has said that he does not consider the military build-up being in anyway an act of war and considers the military build-up at this time as a way of forcing Saddam Hussein to deal with issues which he has refused to do for 13 years," he said.