The EU early-warning mechanism under which national parliaments can object to draft legislation on subsidiarity grounds; if objections reach one third of their votes, the Commission must review the proposal.
In more detail
Protocol No 2 to the EU treaties gives each national parliament two votes (one per chamber in bicameral systems) and eight weeks to send a reasoned opinion. The threshold is one quarter for proposals on police and judicial cooperation in criminal matters. After review the Commission may maintain, amend or withdraw the proposal, giving reasons. A stronger orange card applies under the ordinary legislative procedure when objections reach a simple majority. The yellow card has been triggered three times: Monti II (2012, withdrawn), the European Public Prosecutor's Office (2013, maintained) and the Posting of Workers revision (2016, maintained). The orange card has never been used.