More than 100,000 Poles marched in support of EU membership on Sunday, following a court finding that sections of EU law are incompatible with the country’s constitution, raising fears that the country may eventually exit the group.

Politicians from around Europe were outraged by a verdict by Poland’s Constitutional Tribunal on Thursday, which they saw as undermining the EU’s legal foundation.

Protests were held in over 100 towns and cities across Poland, as well as numerous locations abroad, according to organizers, with 80,000-100,000 people gathered in Warsaw alone, waving Polish and EU flags and yelling “We are staying.”

Former European Council President Donald Tusk, now the leader of the main opposition Civic Platform party, claimed the ruling Law and Justice (PiS) party’s policies put Poland’s future in Europe in jeopardy.

“We know why they want to leave (the EU)… so they may break democratic rules with impunity,” he shouted in front of Warsaw’s Royal Castle, accompanied by thousands of demonstrators and police vans flashing their lights.

PiS claims there are no intentions for a “Polexit.”

Right-wing populist administrations in Poland and Hungary, on the other hand, have found themselves at differences with the European Commission over matters ranging from LGBT rights to judicial independence.

“Just as Brexit suddenly became a fact, something no-one expected, the same thing can happen here,” said Janusz Kuczynski, 59, standing in a street in Warsaw’s historic district leading up to the Royal Castle.

Welcoming the court ruling on Thursday, Polish Prime Minister Mateusz Morawiecki said each member state must be treated with respect and the EU should not be only “a grouping of those who are equal and more equal”.

State-run TVP broadcaster, which critics say focuses heavily on presenting the government’s point of view, ran a news ticker that read “protest against the Polish constitution” during its coverage of Sunday’s events.

Speakers at the demonstrations included politicians from across the opposition, artists and activists.

“This is our Europe and nobody is going to take us out of it,” said Wanda Traczyk-Stawska, a 94-year old veteran of the 1944 Warsaw Uprising against Nazi German occupiers.