Poland is investigating reduced natural gas supplies from Russia’s OAO Gazprom (OGZD) via Belarus and Ukraine, according to the country’s dominant gas company.

Polskie Gornictwo Naftowe i Gazownictwo, or PGNiG SA, got 20 to 24 percent less fuel than it ordered from Gazprom Export over the past two days and is compensating flows with alternative supply, the Warsaw-based company said today in an e-mailed statement. PGNiG shares fell as much as 2 percent, the lowest level since Sept. 1.

“PGNiG is investigating if the supply cut is due to technical or commercial reasons,” the company said.

Gazprom is doing pre-winter maintenance on pipelines and filling Russian storage sites, which is limiting supply to Poland at the level of the end of last week, according to a company official who declined to be named, citing policy. Russia is reducing flows to the European Union to restrict so-called reverse supply to Ukraine, said Ihor Prokopiv, the chief executive officer of UkrTransGas. Poland today halted supply to Ukraine of 4 million cubic meters (140 million cubic feet) a day, he said.

Russia, which meets about 15 percent of Europe’s gas demand through Soviet-era pipelines across Ukraine, halted supplies to its neighbor on June 16 in a dispute over debt and prices, echoing spats in 2006 and 2009 that left European customers short of fuel.

Michael Murphy, a spokesman at RWE AG in Essen, Germany, declined to comment on reverse flow to Ukraine from Poland. RWE started supplies to Ukraine via Poland in April.

Gazprom assumes countries that get their gas via Ukraine understood the possible risks in the spring and filled up storage sites at a faster pace, Sergei Kupriyanov, a spokesman for the Russian pipeline gas export monopoly, said by phone on Sept. 3.

Poland got 9.6 billion cubic meters of gas from Russia last year, or 64 percent of its total use, according to BP Plc’s Statistical Review.

PGNiG shares traded at 4.93 zloty at 2:15 p.m. in Warsaw, after falling as low as 4.91 zloty.

By Marek Strzelecki and Maciej Martewicz