The EU's top court on Tuesday overturned a Hungarian law used to push out a college founded by George Soros, once again putting Budapest at loggerheads with the European Union.

"The conditions introduced by Hungary to enable foreign higher education institutions to carry out their activities in its territory are incompatible with EU law," the European Court of Justice (ECJ) said.

But the ECJ's decision had come to late, said Soros, the 90-year-old Hungarian-born US investor and philanthropist who set up the Central European University (CEU) in the early 1990's,

"We cannot return to Hungary because its prevailing laws don't meet the requirements of academic freedom," said Soros in a statement.

Budapest was originally the home of the main campus, but the university said it was forced to largely move to Vienna in 2019 after falling foul of the new law.

The National Higher Education law written to regulate the sector was widely seen as Prime Minister Viktor Orban directly targeting the CEU.

Soros, who stepped down as chairman of the university's board in 2007, also supports civil society and pro-democracy initiatives critical of Orban's conservative and increasingly hardline government.

The European Commission took Hungary to court over the law and Tuesday's judgement found that Hungary had failed to respect its commitments to the World Trade Organisation.

In particular, Budapest should not have discriminated against colleges such as the CEU by demanding that they offer the same degree courses in their state of origin -- in this case the US -- as in Hungary.

And it should not have required an international education treaty to have been signed between Hungary and the country in which the college was founded.

"That requirement is also contrary to the provisions of the Charter of Fundamental Rights of the European Union relating to academic freedom," the ruling said.

The CEU's president and rector, Michael Ignatieff, told reporters in Vienna that the ruling "renders the law inapplicable in Hungary," and is a "total repudiation of Viktor Orban's legal strategy since 2017".

The university is "now free to re-establish US accredited degree programmes" in Budapest, he said, but added that any such decisions "will take time".

The university's rector described the ruling as a 'complete repudiation of Viktor Orban's legal strategy'
The university's rector described the ruling as a 'complete repudiation of Viktor Orban's legal strategy' POOL / JOHANNA GERON

Hungary's Justice Minister Judit Varga said "as always, Hungary will enforce the judgment of the ECJ in the interest of the Hungarian people", without providing further details.

But in the same statement she insisted: "All universities in Hungary must comply with the law equally.

"It is not possible to create a law that puts (the) Soros University in a more advantageous position than Hungarian universities," she added.

The college, registered in the US state of New York, and providing US-recognised degrees, educated a generation of post-communist elite in Hungary and Eastern Europe.

But Orban's camp saw it as a centre of liberal resistance to his hardline, right-wing rule.

Hungary's ruling Fidesz party and allied pro-government media regularly accuse Soros of working with EU officials against Hungary's national interest, such as orchestrating an influx of migration, but with out offering any evidence.

Brussels, which fears Hungary is sliding toward authoritarianism under Orban, has launched an "Article 7" procedure probing whether Hungary is undermining democratic values.

The European Parliament and some member states are pushing to make payments from the EU budget, of which Hungary is a net recipient, contingent on Budapest fully respecting the rule of law.

And on Tuesday, Soros urged the EU to "make Hungary a test case".

Last week, a major EU report found that in Hungary, "deficient independent control mechanisms and tight interconnections between politics and certain national businesses are conducive to corruption".

Orban is furiously resisting calls for the budget to be linked to rule-of-law concerns, and with Poland, he has threatened to block a huge post-coronavirus rescue package seen as vital to the EU economy.

He has also demanded the resignation of Vera Jourova, one of the EU's vice-presidents, after she quipped that, rather than a self-described "illiberal democracy" Orban had created an "ill democracy".

Other universities and research institutions, including the prestigious Hungarian Academy of Sciences and the University of Theatre and Film Arts, have also protested against moves by Orban which they say restrict their autonomy.