Poland said Gazprom, Russia's state-owned natural gas exporter, continues to overcharge it for deliveries in violation of a recent European court ruling.

PGNiG, Poland’s state-owned energy company, last month won a binding arbitration case against Gazprom in a Stockholm court that ordered the Russian firm to reduce its pricing formula for gas exported to the Central European country under an existing long-term contract.

"Gazprom is not honoring the award issued following the long arbitration process, continuing to issue invoices based on the invalid pricing formula," PGNiG said in a statement on April 24.

Poland in 2014 began talks with Gazprom to change the pricing formula for gas imports as the rise of liquefied natural gas (LNG) altered global energy markets.

Following years of unfruitful talks, PGNiG filed an arbitration case against Gazprom.

The Stockholm court on March 30 ruled in PGNiG’s favor, ordering Gazprom to retroactively alter the pricing formula and pay the Polish firm $1.5 billion for overcharging it since 2014.

Poland’s gas-import contract with Gazprom expires in 2022.

PGNiG is seeking to replace Russian gas with imports from other countries. Poland is already importing LNG from the United States.

With reporting by Vedomosti