The European Commission has begun an anti-trust investigation into Russian gas giant, Gazprom.
Regulators suspect the firm has violated rules by hindering competition, most notably by blocking the free flow of gas across EU member states.
Poland, Hungary and Slovakia are among a total of eight Baltic and eastern European countries concerned.
The commission says Gazprom may have also imposed unfair charges on its customers by linking the cost of gas to oil prices.
If found guilty of abusing its dominant market position, Gazprom could be hit with a heavy fine of up to ten percent of its net profits.