The European Commission has started an investigation into Russia’s natural gas giant Gazprom over concerns that it might be hindering competition in Central and Eastern European gas markets, in breach of EU antitrust rules, the EC said on Tuesday.

“The Commission will treat the case as a matter of priority,” it said.

“The Commission has concerns that Gazprom may be abusing its dominant market position in upstream gas supply markets in Central and Eastern European Member States, in breach of Article 102 of the Treaty on the Functioning of the European Union.”

The Commission is investigating three suspected anti-competitive practices in Central and Eastern Europe.

“First, Gazprom may have divided gas markets by hindering the free flow of gas across Member States. Second, Gazprom may have prevented the diversification of supply of gas. Finally, Gazprom may have imposed unfair prices on its customers by linking the price of gas to oil prices,” the EC said.

Such behavior may constitute a restriction of competition and lead to higher prices and deterioration of security of supply, ultimately harming EU consumers, it said.