By Kate Abnett

(Reuters) -The European Commission on Tuesday proposed legally-binding measures to cut off the European Union's imports of Russian gas and liquefied natural gas imports by the end of 2027, which would end decades-old energy relations with Europe's former top gas supplier.

Here are some details about the proposals, which still need approval from EU countries and the European Parliament.

THE TIMELINE

The ban would take effect in stages. First, from Jan. 1, 2026, the EU would ban imports under any new Russian gas and LNG deals signed before the end of this year.

The EU would then ban imports under short-term contracts from June 17, 2026, for contracts signed before June 17, 2025.

Finally, the EU would ban imports under existing long-term Russian gas and LNG contracts from Jan. 1, 2028. That would sever supply contracts of companies including TotalEnergies and Naturgy, which were designed to extend into the 2030s.

EU LNG terminals would be banned from servicing Russian customers from Jan. 1 2026, under contracts signed after June 17, 2027. Services under existing long-term contracts must halt by Jan. 1, 2028.

Around two-thirds of Europe's Russian gas imports are under long-term contracts. The rest is short-term and spot trades.

QUALIFIED MAJORITY

The ban is based on EU trade and energy law - meaning it can be approved with support from a reinforced majority of countries and a majority of the European Parliament.

A reinforced majority means having the support of at least 15 of the EU's 27 member countries, representing at least 65% of the EU's population.

The Commission chose this route to avoid its proposals being vetoed by Slovakia and Hungary, whose governments have opposed the ban. Sanctions would be the strongest legal basis for banning Russian gas, but require unanimous approval from all EU countries.

FORCE MAJEURE

Spain, Belgium, the Netherlands and France - which import Russian LNG - have said they fully support the ban, while emphasising it must be legally strong enough to avoid exposing firms to penalties or arbitration, EU diplomats told Reuters.

Lawyers have said it would be difficult to eliminate this risk if the EU does not use sanctions. European buyers have "take-or-pay" contracts with Gazprom, which require those that refuse deliveries to pay for much of the contracted gas.

Commission officials said the legal measures will allow companies to invoke the contractual clause of "force majeure" - an unforeseeable event - to break their Russian gas contracts, if the contracts include this clause.

To enforce the ban, the EU will require companies to disclose the volumes, duration and destination clauses of their Russian gas contracts to customs authorities.

REPLACING RUSSIAN SUPPLY

Russia supplied 19% of EU gas imports last year, through LNG and via the TurkStream pipeline supplying Hungary and Slovakia - far below the 45% share Russia supplied before its full-scale invasion of Ukraine in 2022.

Russia's share is expected to fall further, to 13% this year.

The Commission said its proposals would not threaten Europe's energy supplies, since EU countries have spare LNG import capacity or alternative pipeline routes through which they can import non-Russian gas.

The EU has infrastructure capacity to import 250 billion cubic metres of LNG per year, but last year used less than half of this, the Commission said.

To replace Russian supplies, the EU has signalled willingness to increase LNG imports from the United States, which Brussels is under pressure from President Donald Trump to do.

For Hungary and Slovakia, switching to alternatives will cost. Russian pipeline gas was sold at a 13-15% discount to other options last year, according the Center for the Study of Democracy.

OIL, NUCLEAR

Unlike with gas, the EU has imposed sanctions on most Russian oil imports, with exceptions for Slovakia and Hungary, which still import more than 80% of their oil from Russia.

The Commission proposed a legal obligation on Tuesday for Slovakia and Hungary to produce national plans for how they will quit Russian oil by end-2027. Just 3% of total EU oil imports now come from Russia.

Brussels will also propose measures to limit the EU's reliance on nuclear fuel from Russia, but has not confirmed a date for these proposals.

(Reporting by Kate Abnett; editing by David Evans)