The German state competition body, the Bundeskartellamt, has asked the country's two largest energy suppliers, E.ON and RWE, to respond to its queries over alleged overpricing in the country's energy market.

The two companies have until mid-September to provide the regulator with reports on the matter. Earlier this month, an association of industrial and commercial power users, VIK, filed a complaint accusing the two utilities of abusing their dominant position in the marketplace. The allegations center on the recently-introduced CO2 emissions trading scheme, which VIK believes may be being misused by the E.ON and RWE as an excuse to charge higher prices.

According to a Financial Times Deutschland report, Germany’s environment minister Juergen Trittin told a state broadcaster that he supported VIK’s complaint. Mr Trittin reportedly suggested that, if the companies were adding the cost of CO2 allowance credits into wholesale prices, that amounted to market manipulation.

The CO2 credits were distributed free of charge to utilities by the EU, but their value has risen sharply over the course of the year. The trend has been exacerbated this summer as power output from renewable sources has declined due to the hot weather and lack of rainfall in southern Europe.