The Prime Minister says the Government will wait until it sees clear evidence about the merits of lowering the blood alcohol level for driving before it makes any decision.
Parliament is to debate a member's bill in the name of Iain Lees-Galloway after it was pulled from the ballot last week.
It proposes to cut the legal limit from from 80 milligrams of alcohol per 100ml of blood, to 50ml.
Mr Key says the Government has asked for more research to be done before deciding whether the current limit should be lowered.
He says the Labour Party bill is effectively redundant, because if a change is needed, it will done by government legislation.