Slovakia and Hungary say they will not support sanctions against Russian energy, including on oil imports, which the European Union has indicated it is on the cusp of proposing to punish Moscow for invading Ukraine.
The two countries say they are too reliant on Russian oil and there are no immediate alternatives.
Slovak Economy Minister Richard Sulik said it would take years for the country's sole refiner, Slovnaft, to switch from Russian crude to another source of oil.
Hungary is also heavily reliant on Russian oil. Foreign Minister Peter Szijjarto said Hungary will not vote for any sanctions "that will make the transport of natural gas or oil from Russia to Hungary impossible."
Speaking on May 3 in Kazakhstan, Szijiarto said it would be impossible for Hungary and its economy to function without Russian oil.
"The point is simple, that Hungary's energy supply cannot be endangered because no one can expect us to allow the price of the war to be paid by Hungarians," Szijjarto said on May 3 in Kazakhstan.
The European Commission's new proposals for sanctions could include a phased-in embargo on Russian oil. The 27 member countries are likely to start discussing them on May 4, but it could be several days before the measures are endorsed and enter into force.
EU foreign policy chief Josep Borrell said earlier on May 3 that the bloc's executive branch is close to proposing the new sanctions and the package would include oil imports.
"We are working on the 6th package of sanctions which aims to de-SWIFT more banks, list disinformation actors and tackle oil imports," Borrell said on Twitter.
SWIFT is used by thousands of financial institutions in more than 200 countries, including Russia, to facilitate cross-border money transfers. Several Russian banks were excluded from the SWIFT system in a previous package of sanctions.
Countries in favor of an oil embargo say it would cut off funding that Russia is using to finance the war. Poland is among the EU member states that have spoken in favor of an oil embargo, while others, most notably Germany, have been wary of the economic fallout of a ban.
But German Economy Minister Robert Habeck, said that Berlin "is not against an oil ban on Russia."
Habeck made the comment on May 2 in Brussels before talks with his EU colleagues. He said it would be a heavy burden, but added, "We would be ready to do that."