Russia's Federal Antimonopoly Service (FAS) has opened an antitrust case against aluminum producer Rusal over what it said were unfair pricing terms for domestic customers, Interfax reported Wednesday, escalating a dispute over how the company prices metal sold within Russia.

The FAS said it had previously instructed Rusal to amend the terms of its aluminum supply contracts for Russian customers, but the company failed to comply despite twice requesting extensions to the deadline.

According to the regulator, Rusal's pricing formula for domestic buyers includes a regional premium based on a European benchmark, even though Russian-produced aluminum is now shipped primarily to Asian markets.

"The pricing model shows signs of violating antitrust legislation because it places Russian processors at a disadvantage, with domestic companies paying more for aluminum than foreign buyers," Interfax quoted the FAS as saying.

The regulator said aluminum prices feed through into the cost of a wide range of products, from packaging and construction materials to equipment for the power sector.