After Brexit, the EU member states made a commitment to unity in their Rome Declaration of March 2017. They also indicated the possibility of creating a ‘two-speed’ or ‘multi-speed’ Europe, with members cooperating in areas of interest and forming alliances on issues ranging from refugees to defence. That move was highly criticised by Poland, which saw the danger it could face from the creation of ‘second-tier’ membership and the abolition of European unity as a core EU goal.

After Poland became an EU member in 2004, it rose to be an important player and respected ally, and was often framed as a success story of European integration. Democracy flourished, and the economy grew stronger, thanks to EU structural and regional funds. Poland’s GDP rose from US$66 billion in 1990 to US$470 billion in 2016, and it is the biggest beneficiary of EU spending. In 2015, it received over €13 billion (3.25% of its GNI); its total contribution to the EU in 2015 was €3.7 billion (0.90% of GNI).

Despite over a decade of beneficial and fruitful relations between Warsaw and Brussels, Poland is causing EU officials concern as Europe confronts the combined challenges of terrorism, large influxes of refugees, and the uncertainties of Brexit.

With the UK leaving, Poland will lose one of its main allies. But, with 38 million inhabitants, it will also be elevated to the fifth-largest country in the EU, giving it more influence in EU institutions. It had been hoped that Poland would join the engine-room pair of Germany and France to foster a strong, unified post-Brexit EU, actively contributing to reform and helping find solutions to current challenges.

Since taking power in 2015, the Polish national-conservative party, Prawo i Sprawiedliwość (Law and Justice; PiS), has regularly attacked EU institutions and politicians. After initially vowing to improve relations with Berlin, Warsaw stepped up criticism of the German government and is now considering requesting reparation payments for World War II. Emmanuel Macron got also caught in the crossfire when he criticised the Polish government for rejecting reform of the so-called posted-workers directive. Polish prime minister Beata Szydło called the French president ‘arrogant’, claimed he was ‘lacking political experience’, and pointedly declared that it wasn’t France that would decide the EU’s future. Poland also rejected the EU’s plans for a quota system to allocate refugees to member states, drawing strong criticism from other members.

However, PiS is not an anti-EU party per se. It wants changes—mainly returning powers to the member states and limiting the EU’s jurisdiction. And despite the current tensions, Poles are among the EU’s strongest supporters. In a recent poll by the Pew Research Center, 74% of Poles expressed a favourable view of the EU—the highest of all the nations surveyed. At the same time, national polls indicate continued support for PiS, despite its quarrels with the EU and the growing anti-government and pro-Europe demonstrations in Polish cities. Those results show that people’s backing of domestic policies doesn’t affect their support for the EU, and vice versa.

Tensions between the European Commission and PiS started heating up a year ago after the commission expressed serious concerns about the state of the rule of law and press freedom in Poland. In July 2017, when PiS passed three bills that attempted to put the judiciary largely under government control (see here for more details), the commission threatened to invoke Article 7 of the Lisbon Treaty. It was the first time that an EU member was threatened with such action and reflected how seriously the commission views breaches of major European values.

The commission gave Poland one month to respond to its inquiry on the state of the rule of law. Invoking Article 7 could see Poland stripped of its voting rights, but that will only happen if there’s a unanimous vote against it by all member states. That’s not likely, as Hungary’s prime minister, Viktor Orban, has already declared solidarity with Poland. The Polish government, meanwhile, let the deadline to answer pass, and sent a 12-page submission explaining why it considered the inquiry groundless. The commission is yet to publish a detailed response.

PiS is now also at odds with the European Court of Justice, after it ordered Poland to immediately stop logging in Białowieża Forest, a UNESCO heritage site on Polish and Belarusian territory, and Europe’s oldest forest. The Polish government claims that logging is necessary to fight a beetle outbreak, but the EU says the site is protected under European environmental law. Poland is ignoring the ruling and has continued logging, which has also sparked protests at the site.

Member states need to realise that the EU is a bound community of shared values and interests, and not an association where benefits—and solidarity—can be cherrypicked. The actions of PiS have brought uncertainty to the EU when it most needs unity and stability to confront increasing security challenges.

Correction: An earlier version of this post included an incorrect figure for Poland’s GDP in 2016. The error occurred at the editorial stage.