Polish Prime Minister Donald Tusk on Friday warned against Hungary’s potential expulsion from the Schengen Area – a measure proposed as punishment after Budapest eased its entry rules for Russians.

Last month, Budapest extended its special visa regime – the National Card system – to include Russian and Belarusian nationals. The scheme allows foreigners to work in Hungary for up to two years and paves the way for them to apply for permanent residency.

Hungary’s move garnered attention after European People’s Party Chairman Manfred Weber criticized it in a letter to European Council President Charles Michel, claiming the new scheme could make it easier for “Russian spies” to enter the bloc.

Earlier this week, a group of 67 members of the EU Parliament sent an official letter to European Commission President Ursula von der Leyen, demanding Hungary be punished if it refuses to change its visa policy. One of the signatories, Finnish MP Tytti Tuppurainen, proposed introducing border controls with Hungary and ultimately excluding it from the Schengen Area if its new visa requirements are not amended.

According to Tusk, drastic measures are not advisable. “Exclusion from the Schengen Area is actually a prelude to exclusion from the EU,” he said at a press briefing on Friday.

“I would be careful here… I put a lot of effort into removing [Hungarian Prime Minister] Viktor Orban and his party from the international group... but I would be careful with motions to expel countries from the EU,” Tusk, an outspoken critic of what he has called Budapest’s “Russian position,” added.

He said he did not know the full details of Hungary’s visa decision, but “at first glance… it seems that provisions of European law have been violated along with regulations related to risks to the security of the Schengen countries.” Tusk noted that Hungary is not the only EU country that grants visas to Belarusians and Russians, so punishing it would not prevent them from entering the bloc.

Poland has been a key backer of Kiev amid the conflict between Russia and Ukraine, sending military aid and serving as a hub for Western weapons supplies. Hungary, however, has opposed funding and arming Kiev.

Orban has been calling for a diplomatic solution to the conflict, and embarked on what he called a Ukraine ‘peace mission’ last month, holding talks with Kiev and Moscow to urge them to negotiate. His actions, including a meeting with Russian President Vladimir Putin, drew criticism within the EU, with some members calling for the rotating EU presidency which Hungary currently holds to be revoked.

Brussels has so far responded to criticism of Hungary’s new visa rules by asking Budapest to officially explain the move. The EU is expected to address the issue at its summit in October.