This way Lithuania wants to have a mechanism for economic sanctions against Russia and Belarus in case the EU fails to extend its own.

I don’t see how this would work in practical terms.

So, okay, right, at the moment a unanimous decision by the EU is required to impose any sanctions.

However, the reason the EU requires a decision to be made at the EU level to impose trade sanctions isn’t just some arbitrary call. It’s because one requires practical enforcement of those at the European Union Customs Union border. If you’re going to say “buying Russian vodka is not allowed”, then that’s where you catch that Russian vodka.

Inside a customs union, there’s no customs checking. If, say, Hungary is letting Russian vodka roll in, then that vodka can pass into other EU members from there.

I could maybe see some system where a unanimous vote isn’t required, but the whole EUCU enforces the sanctions. Say a supermajority of two-thirds of EU members voting for sanctions mean that the whole of the EUCU is obliged to enforce sanctions. Or maybe a system of incentives and disincentives by other members could be used to get Hungary to go along with the sanctions.

But I think that any point where part of the EUCU is enforcing sanctions would require doing customs checking at internal EU borders, and that seems like it’d dick things up economically in the EUCU.

Maybe it’d be possible to do some kind of best-effort checking, like just pass a law in Lithuania and then randomly check retail stores to try to find stores breaking it, have some huge fine if someone’s caught?