Two weeks ago, Poland’s highest court, the Constitutional Tribunal, issued a ruling that claims its decisions have priority over the treaties that undergird the European Union. That may sound like a minor legalistic spat, but it’s actually quite significant.

While the EU is made up of sovereign member states, it does possess binding authority over them in a variety of areas, according to the treaties Poland once signed and now violates. Such a challenge to the authority of the EU is unprecedented in recent history. If the Tribunal’s ruling holds, it could lead to similar actions by other member states and—perhaps—ultimately a reversal of Europe’s increasing integration.

The quality of democracy in Poland has precipitously declined in the past decade as its ruling right-populist Law and Justice Party (PiS) has chipped away at democratic institutions, rights for minorities, and the independence of the press.

In the worst offense, PiS severely undermined the rule of law by forcing the retirement and replacement of many judges with party loyalists in 2017 and establishing a new disciplinary body to punish judicial officials. That body was formed in order to increase accountability to the elected parliament and in doing so has transformed the courts into an arm of parliament’s leading political party, PiS.

The EU’s highest court, the European Court of Justice, ruled that such actions violated the independence of courts and thus the principle of rule of law upon which the European Union was founded. In response, Poland’s Constitutional Tribunal issued its controversial ruling last week, setting the stage for a conflict between EU and Polish political leadership.

But some in the European Union seem reluctant to make a fight of Poland’s democratic backsliding. Ahead of a summit of EU leaders, outgoing German Chancellor Angela Merkel advised the European Commission, the EU’s executive branch, to proceed with caution and seek compromise. She claimed that starting a lengthy legal battle was “not a solution.”

It’s certainly true that existing EU institutions face an uphill battle in nudging Poland away from its democratic decline. To issue robust sanctions against Poland would require unanimity among all member states except Poland. Hungary, another country experiencing severe democratic backsliding, has made clear that it would exercise its veto power to prevent that from happening.

But that doesn’t mean the EU is powerless. Poland is the largest net economic beneficiary of membership in the EU, and some COVID relief aid has been withheld in response to the creation of “LGBT-free zones” in Poland. Some of those “zones” have ended their discriminatory laws in response. In other words, where pressure has been applied, it has worked. Continuing to exercise the options available, however limited, has merit.

Given Poland’s reliance on the EU, something like a “Polexit” from the EU is highly unpopular in the country. European leaders have little reason to fear another withdrawal—it’s the continued membership of states which erode the Union from within that should scare them.

Moreover, contrary to Ms. Merkel’s conflict-averse recommendation, embracing a confrontation with Poland could be productive rather than destructive. Such a showdown would force the EU to sort out its mission and core purpose: either economic arrangement or alliance for democracy.

The Maastricht Treaty—which established the EU as a successor to the European Economic Community in the 1990s—and the 2009 treaty of Lisbon clearly state that among the Union’s core values are democracy, human rights, and the rule of law, not just economic cooperation. Working through the tensions over sovereignty and the extent to which Europe should integrate could move the European Union away from the odd fence-sitting space it currently occupies.

In response to the Polish Constitutional Tribunal’s decision, Belgium’s Prime Minister Alexander De Croo said, “If you want to be part of a club and have the advantages of a club, you must play by the rules.” Poland has decided that it won’t play by the rules, but it’s not necessarily the case that it “must,” especially if European leaders let the Law and Justice Party get away with flouting, well, law and justice. Only by decisively enforcing its rules through available mechanisms can the EU both ensure those rules are followed in the future and clarify the purpose of European integration.