The deadline will ramp up tensions between the EU and Poland over the Polish government’s overhaul of the judicial system, which Brussels says undermines the independence of the judiciary.
Last week the Court of the Justice of the European Union (CJEU) imposed interim measures on Poland until a verdict is issued in a rule-of-law case brought against Poland by the European Commission.
Under the interim measures, announced on July 14, Poland must suspend the operations of the Supreme Court's Disciplinary Chamber, a body the Commission has said lacks independence.
Announcing the deadline European Commission Vice-President Vera Jourova said: "The European Commission decided today to empower Commissioner (Didier) Reynders, as commissioner for justice, to adopt measures to induce the Republic of Poland to comply with an order and a judgement of the Court of Justice. We have sent a letter on this matter.
"We have asked Poland to confirm to the Commission that it will fully comply with the order of the court of the 14th of July on the disciplinary chamber,” she added. “Poland needs to inform us about the measures foreseen to that effect by the 16th of August as requested by the Court.
"Failing that, the Commission will request the European Court of Justice to impose a penalty payment on Poland."
Underlying the fact that Brussels appears to want to take a hard line with Poland, European Council Ursula von der Leyen took to Twitter to say that the EU will use all powers at its disposal.
"Today we sent a letter to Poland, asking Poland to explain how it applies the interim measures and recent ruling of the CJEU to safeguard judicial independence," she wrote. "The @EU_Commission will not hesitate to make use of its powers under the Treaties." (PAP)