Since this is Union Law, and according to the treaties, a party in Poland could escalate such a copyright case to the ECJ, which could then overrule any Polish

Since this is Union Law, and according to the treaties, a party in Poland could escalate such a copyright case to the ECJ, which could then overrule any Polish higher court. The thing is that the ECJ requires (or advices) Poland courts to comply to its decisions, but cannot actually enforce them, which is totally up to the country. So if Poland decided to go on its own on this, theoretically it could since the EU states are sovereign, but in practical terms, and this is a really fuzzy divide, Poland would not do it if it wants to remain a politically "healthy" member of the EU.