The four prime ministers discussed the Nord Stream 2 project of Russia's Gazprom and its partners during their meeting in Tallinn.
"We believe that this is not just an economic, commercial project. This project can have a negative impact on the gas market of the European Union and I have reaffirmed the Lithuanian position," Lithuanian Prime Minister Saulius Skvernelis said at a news conference in the Estonian capital.
"Lithuania has joined legal procedures regarding Opal. We support Poland in the legal proceedings against the European Commission," he said.
Polish Prime Minister Beata Szydlo said that Nord Stream 2 was a political project.
"We did speak about Nord Stream 2 and I took the opportunity to thank the prime ministers of Lithuania and Latvia for joining Poland in its claim in Opal. We always underline very strongly that it's a political project," she told the news conference.
Latvian Prime Minister Maris Kučinskis also said that Latvians "think that it's a political project, not an economic, commercial project".
His Estonian counterpart, Juri Ratas, said, "We believe that Nord Stream 2 does not meet the energy union strategic objectives and it is definitely harmful to our energy unity."
The European Commission last autumn approved an increase in Gazprom's quota for the use of Opal, a gas pipeline in Eastern Germany that is connected to the Nord Stream pipeline between Germany and Russia across the Baltic Sea. Critics say that increased use of Opal and Nord Stream may reduce gas transit flows via Poland and Ukraine.