EU antitrust regulators have charged Russia's Gazprom with abusing its dominant position in Poland, Hungary and six other nations in Eastern Europe following over two years of investigation.
The European Commission (EC) said that the state-controlled energy giant, a key supplier of energy to Europe despite frequent political disputes, had hindered cross-border competition across the region and overcharged in five of the countries.
The EC said in a 22 April statement: "Gazprom now has 12 weeks to reply to the Statement of Objections and can also request an oral hearing to present its arguments. The Commission will fully respect Gazprom's rights of defense and carefully consider its comments before taking a decision.
"Sending a Statement of Objections does not prejudge the final outcome of the investigation."
European Competition Commissioner commented: "...We find that it (Gazprom) may have built artificial barriers preventing gas from flowing from certain Central Eastern European countries to others, hindering cross-border competition.
"Keeping national gas markets separate also allowed Gazprom to charge prices that we at this stage consider to be unfair.
"If our concerns were confirmed, Gazprom would have to face the legal consequences of its behaviour."
Vestager's decision to move against Gazprom came just a week after she charged US tech giant Google with abusing its market power and more than two years after Brussels began probing the Russian firm.