The European Union launched a. legal attack on Gazprom on Wednesday , stoking tensions . with Moscow as it accused the Russian gas giant of overcharging . buyers in Eastern Europe and hindering competition . European Commission antitrust chief Margrethe Vestager said . Gazprom was barring EU clients from selling on its gas to other . states - a particular concern in recent efforts to aid Ukraine - and pressuring governments to back its pipeline interests . Russian Foreign Minister Sergei Lavrov said that the charges were 'absolutely unacceptable ' . The European Union launched a legal attack on Gazprom on Wednesday , stoking tensions with Moscow as it accused the Russian gas giant of overcharging buyers in Eastern Europe and hindering competition . European Commission antitrust chief Margrethe Vestager ( pictured ) said Gazprom was barring EU clients from selling on its gas to otherstates . State-controlled Gazprom is a vital supplier of energy to . Europe despite the EU 's frequent political disputes with Moscow . The Commission 's investigation , opened in September 2012 , . had initially covered Poland , the Czech Republic , Slovakia , . Hungary , Bulgaria , Estonia , Latvia and Lithuania . Relations with Russia , and Gazprom in particular , have since . been poisoned more by the East-West confrontation over Ukraine . 'Gazprom is dominant in all these markets , ' EU Competition . Commissioner Vestager told a news conference . 'Our preliminary . view alleges that Gazprom is abusing this position . ' 'Gazprom has been able to charge higher prices in some . countries without fearing that ... gas would flow in from where . prices were lower , ' she said of contracts with the three . ex-Soviet Baltic states and formerly communist Poland and . Bulgaria . Vestager said prices in some countries were as much as 40. per cent higher than in others . Lithuanian President Dalia Grybauskaite welcomed the . charges , saying : 'The era of Kremlin-backed political and . economic blackmail draws to a close . ' Russian Foreign Minister Sergei Lavrov said that the charges were 'absolutely unacceptable ' Noting the investigation had begun before Russia annexed . Crimea from Ukraine , Vestager said 'this case is not political ' but acknowledged some would see political elements in it . Gazprom responded by calling the charges , to which it has 12. weeks to respond , 'unfounded ' and saying it expected a. resolution within the framework of previous undertakings between . the Kremlin and Brussels 'on the intergovernmental level ' . Russian Foreign Minister Sergei Lavrov said on Wednesday that the EU charges against Gazprom were an unacceptable attempt to retroactively apply the bloc 's latest energy rules to earlier contracts . Asked to comment on the case , Lavrov said in an interview with three radio stations : 'All contracts in effect now that Gazprom signed with its partners , were signed with full respect of the legal regime that existed in the EU at the time . 'After the EU adopted the so-called third energy package ... there have been attempts , and they continue now , to retrospectively , retroactively apply those requirements to old contracts as well . That is absolutely unacceptable . ' The EU has brokered deals to keep gas flowing to Ukraine . despite the conflict between Kiev and Moscow , but efforts to . supply gas via eastern EU states have been hindered by contracts . with Gazprom that prohibit the re-export of Russian gas . Gazprom had also pressured Poland and Bulgaria into . accepting unfavourable terms over gas pipeline control and . construction , the commissioner said . The decision to move against Gazprom comes a week after . Vestager charged U.S. tech giant Google with abusing . its market power , following five years of hesitation by her . predecessor . She said , however , that in other cases she would be . willing to negotiate with firms without pressing charges . The Dane has appeared determined to challenge big corporate . powers since taking on the powerful post in November , regardless . of past offers of compromise from both Google and Gazprom . Despite insisting she would look only at the legal merits of . a case that focuses on Gazprom 's pricing policies for different . customers , the accusations will not ease frictions with Moscow . over Ukraine in which gas supplies have played a major role . Gazprom offered concessions to Vestager 's predecessor last . year in a bid to settle the case and avoid a possible fine but . talks failed over its refusal to cut prices in eastern Europe . The Russian behemoth , with annual sales of some $ 100 . billion , supplies about 30 per cent of the 28-nation EU 's natural . gas . It has been under investigation since September 2012 , . including for hampering the flow of gas across Europe . Vestager can order companies to change their business . practices and is theoretically able to levy fines of up to 10. per cent of their annual global turnover .
Antitrust chief said Gazprom is barring EU clients from selling on its gas . Russian Foreign Minister Sergei Lavrov said charges were 'unacceptable ' 'Era of Kremlin-backed economic blackmail draws to a close ' - Latvia .