Poland's gas monopoly PGNiG says it has filed a lawsuit against its Russian supplier Gazprom with an international tribunal in a price dispute, AP reported.

State-owned PGNiG said Tuesday, February 21 that the reason was a change in the pricing within a long-term deal concluded in September of 1996. It filed the lawsuit with the Arbitration Tribunal in Stockholm. It refused to give more details.

Gazprom in January eased prices for some of its clients in Western Europe, but not for PGNiG, which has been lately asking for price cuts.

Under the current deal, Poland's imports of Russian gas were more than 318 billion cubic feet (9 billion cubic meters) in 2011 and were to rise to 360 billion cubic feet through 2022, but the prices was not released to the public.