The European Commission said that Public Power Corp (PPC) might have undercharged by €17.4M ($24.5M) and it would investigate the case under European Union state aid rules.

The Commission said in a statement that it would also investigate allegations that state-owned Public Gas Corp paid the construction costs of a gas pipeline belonging to Aluminium of Greece, southeast Europe’s biggest aluminium smelter. It did not identify the complainants.

The Commission has already investigated a number of complaints that the aluminium company received privileges before Greece joined the EU in 1981. It has taken a preliminary view that due to the timing, those privileges need not be repaid.

Aluminium of Greece is a unit of the Mytilineos Group, which aims to become PPC’s biggest rival in the Greek electricity market.

PPC said last July it would seek arbitration to resolve a dispute with Aluminium of Greece, which has refused to accept a 10% increase in PPC’s electricity prices, citing profitability concerns amid a slumping metals market.