The Hungarian parliament, dominated by supporters of Prime Minister Viktor Orbán, has voted overwhelmingly for a set of constitutional amendments that opponents, including the EU, the U.S. government and human rights groups, fear will undermine the country's 24-year-old democracy.
The concern is that the enlargement of the EU since 2004 has brought into the bloc central and east European countries that do not fully share the same norms of democracy, human rights and the rule of law as Germany, France, Britain or other powers.
If left unchecked, that could undermine the values that have bound the EU together since its founding, officials warn.
Orbán and senior Hungarian officials have lined up to offer reassurances about Monday's constitutional shake-up, denying there is any threat to democracy or judicial independence.
But it is not the first time Orbán has rattled the EU's cage and there is alarm in Brussels at the latest move, which follows changes last year to other sensitive media and banking laws.
European Commission President José Manuel Barroso issued a statement immediately after the Hungarian vote saying the amendments "raise concerns with respect to the principle of the rule of law", and EU legal experts have begun examining the changes to see where Hungary may have violated EU law.
Guy Verhofstadt, the leader of the Liberals in the European Parliament, said time was running out for Orbán.
"Orbán has been warned many times that the values of the union he joined are not to be abused or ignored," he said. "It is time to see the Orbán regime for what it is, a government set on imposing the will of a majority over a minority."
German Foreign Minister Guido Westerwelle, who had what officials described as a stormy meeting with Hungary's president in Berlin on Tuesday, said he could not hide his concern at the way Orban and his government were operating.
"It is important that every country in the EU understands that we belong to a community of values," he told a group of reporters on the sidelines of a meeting in Brussels on Monday.
"I do not have to deny that I am concerned about these latest developments in Hungary. I express my concern."
But for all the frustration and denunciation, there is little the European Union can do with any alacrity or immediacy that might make the mercurial Orbán sit up and listen.
The way the EU operates is based largely on consensus among the 27 member states. If a country is deemed to have fallen out of line there are legal and other steps that can be taken, but it takes time to build support for them and make them bite.
In the case of Hungary, and similar stand-offs with Romania and Bulgaria in recent years, the first response from fellow member states and the European Commission, the EU's executive, tends to be political pressure or moral persuasion to try to make the government in question alter its behavior.
While that can have an impact, as was the case in Romania last year when the prime minister sought to oust the president, in tricky cases of law backed by democratically elected parliaments, as in Hungary, it is much more difficult.
"There's a shortage of what the EU can do to ensure that democratic practices, or democracy itself, is not reversed," said Corina Stratulat, an expert in the politics of central and eastern Europe at the European Policy Centre, a think tank.
"There is an awareness that something has to change in terms of enhancing the tools that the EU has at its disposal to influence situations like we've seen in recent years."
Beyond political pressure, the Commission can launch what is known as an "infringement proceeding" against a country. But that relies on having hard evidence that EU law has been breached and pursuing the case through tortuous legal channels.
Even under a best-case scenario, infringement proceedings can take up to a year. While the Commission may already have evidence to move against Hungary in the latest incident, it is not going to deliver any change in Budapest anytime soon.
"To prove that they've breached a law is very difficult," said an EU official familiar with the process. "Infringements can and do work, but it is not a quick-reaction tool."
One article of the treaty that binds EU member states together does allow for the near-immediate sanctioning of a member country, but it requires unanimous backing of all other member states and is considered a "nuclear option".
In a letter last week, Westerwelle said the EU needed a way of taking more immediate action against countries that do not respect EU "norms", without referring to any country.
Barroso made a similar call in a speech last year, saying threats to the "democratic fabric" in some EU states meant an alternative was needed between the soft power of political pressure and the "nuclear option" of article 7 of the treaty.
But any move along those lines is a long way off. For now, the EU needs to find a way to bring pressure to bear on Hungary, possibly by working with the International Monetary Fund to withhold financial assistance, and make it shift course.
Otherwise, analysts say, it will find itself with a growing problem of trying to enforce democracy in some of the central and Eastern European countries that the EU was so keen to draw into the heart of Europe after the fall of communism.
"What all this has shown is that the assumption that once you become a member you are fully democratized and there's no going back has been completely questioned," said Stratulat of the European Policy Centre.
"Democracy and democratization are forever a work in progress."