Hungary still gets the vast majority of its natural gas from Russia; Slovakia a significant portion.

After the ban was approved, the governments of both countries indicated that they would sue the EU.

Now, the Hungarian government under Prime Minister Viktor Orban has taken the matter to the European Court of Justice (ECJ). On February 2, it filed a legal challenge to the ban, arguing?the EU had violated its treaties when taking the decision.

The lawsuit hinges on three arguments, according to Hungarian?Foreign Minister Peter Szijjarto:

Hungary is no stranger to suing EU institutions. A dozen cases filed by Budapest against various EU bodies are currently pending before the ECJ.

While the court has frequently ruled against Hungary in the past, some legal experts say this case may be different.

"To me, this looks like a legal proceeding which Hungary might have a chance of winning," Viktor Szep, a legal scholar with a focus on European law at the University of Groningen, told DW.

A seemingly technical question could be decisive: Is the Russian gas ban really a trade measure? Or is it a foreign policy sanction dressed up as a trade measure?

The distinction matters because EU sanctions require unanimous consent from all 27 member states. By treating the gas ban as a trade policy matter, the Commission was able to pass it with a qualified majority vote (15 out of 27 member states, representing at least 65% of the EU's population), effectively sidelining objections from Budapest and Bratislava.

Szep argues that by passing the ban as a trade measure, the EU broke with its institutional practice of passing sanctions unanimously — be they against Russia or against countries like Venezuela or Iran.

"It is difficult to argue in favor of the Commission, because all of those were adopted unanimously," he said.

So, why was this ban treated differently?

A key difference lies in the planned duration of the measures.

"Sanctions are temporary measures which are aimed to expire once the triggering factor disappears," said Agata Loskot-Strachota, an energy policy analyst with the Warsaw-based Centre for Eastern Studies, in an interview with DW.

The Russian gas import ban, by contrast, is set to permanently change the EU's energy supply, as European Commissioner for Energy and Housing Dan Jorgensen made clear in an interview with Euronews in December: "Even when there's peace, we won't buy Russian gas again."

The principle of legal coherence — the idea that all EU policies should be aligned — could strengthen the Commission's case, Lukas Schaupp, a PhD researcher at the European University Institute in Florence, told DW. "The ban can be understood as a logical extension of the EU's sanctions regime into the closely related field of external trade policy," he said.

Commissioner Jorgensen defended the ban as "100% legally sound" and necessary to end Russian "energy blackmail" of EU countries, adding that all 27 members must implement the ban whether they voted for it or not.

Some observers think, however, that the EU was also deliberately avoiding a situation in which one country could veto the import ban.

"The political aim was to not to have to wait for everyone to agree, because it was clear that unanimity was very difficult to achieve," said Loskot-Strachota. "Europe had to become quicker and more effective in achieving its goals. These goals are defined by a big majority, of which Hungary, unfortunately, is not a part."

Hungarian?Prime Minister Orban has maintained close ties with Russian President Vladimir Putin, even after the invasion of Ukraine, and has repeatedly blocked or delayed EU measures aimed at putting pressure on Putin's regime.

This is what the EU wanted to prevent this time, said Loskot-Strachota.?"I think this regulation is a way for the EU to limit opportunities for Russia to apply the 'divide and conquer' strategy," she said.

The ECJ often takes years to reach a final ruling. And even if the court ultimately decides to side with Hungary, that would not automatically mean that it would revoke the gas ban in practice.

"In the past, the ECJ has often stated — particularly with regard to investment certainty — that a measure may be annulled, but its effects remain in force, to avoid major economic disruption," Schaupp told DW.

By the time of the ruling, member states and companies will have taken measures to eliminate their reliance on?Russian gas, from building infrastructure to signing contracts with alternative suppliers.

For now, the ban remains in effect, meaning that by the end of?2027 at the latest, all EU member states have to stop buying Russian gas — including Hungary and Slovakia.

Edited by: Aingeal Flanagan