Eurosceptic and far-right parties have seized ground in elections to the European parliament, in what France's PM has called a "political earthquake".
The French National Front and UK Independence Party both performed strongly, while the three big centrist blocs in parliament all lost seats, the BBC reports.
The outcome means a greater say for those who want to cut back the EU's powers, or abolish it completely.
But EU supporters will be pleased that election turnout was slightly higher, at 43.1 percent according to provisional European Parliament figures.
That would be the first time turnout had not fallen since the previous election - but would only be an improvement of 0.1 percent.
"The people have spoken loud and clear," National Front (FN) president Marine Le Pen told cheering supporters in Paris.
"They no longer want to be led by those outside our borders, by EU commissioners and technocrats who are unelected. They want to be protected from globalisation and take back the reins of their destiny."
Provisional results suggested the FN could win 25 European Parliament seats - a stunning increase on its three in 2009.
The party also issued an extraordinary statement accusing the government of vote-rigging.
Across the board, the centre-right European People's Party (EPP) was set to win 212 out of the 751 seats, with 28.23 percent across the bloc, according to estimated results issued by the European Parliament. That would make it the biggest group - but with more than 60 seats fewer than before.
That put it ahead of the Socialist group with 186 seats (24.77 percent), Liberals with 70 (9.32 percent) and Greens 55 (7.32 percent).
EPP leader Jean-Claude Juncker insisted most had voted to be a part of Europe.
"The extreme right, contrary to what some of the media has said, did not win this election," he said.
"We will have a clear pro-European majority in this house," added the man who is the frontrunner to be the next president of the European Commission.
The Eurosceptic Europe of Freedom and Democracy group, incorporating the UK Independence Party (UKIP), appeared to have about the same number of seats as last time.