This study examines when and why members of the European Parliament (EP) use parliamentary questions as a form of fire alarm oversight. We argue that the multilevel nature of the EU political system allows members of the EP from national opposition parties to use parliamentary questions to alert the European Commission to governments' failures to implement EU policy. Representation in the EP provides the only avenue for such oversight for national opposition parties. Using a new sample of EP parliamentary questions, we demonstrate that MEPs from national opposition parties are more likely to alert the Commission to violations of EU law in their own member states. These parliamentary questions may lead the Commission to take legal action against member-state governments.