An accusation by environmental law firm Client Earth that the Bulgarian government has been flouting the law on state aid has been firmly denied.

The London-based legal firm asserts that Bulgaria has given $1.5bn in illegal aid to coal-fired and other power plants, according to a complaint filed with the European Commission.

EU state aid rules are designed to facilitate the transition to a lower carbon economy , with provision for some fossil fuel support in order to ensure energy security as the system shifts.

ClientEarth lawyer Sam Bright (left) said the activist lawyers had spent more than a year investigating Bulgaria’s practice of requiring public power provider NEK and distribution companies to buy all the electricity produced by plants classified as “high-efficiency co-generation” that produce heat as well as power.

These operators are paid a surcharge, which comes from a levy on consumer bills.

“Bulgaria is giving these plants an unfair and unlawful subsidy, which is helping to prop up coal power plants, amongst others, and hindering the transition from fossil fuels to cleaner energy,” Bright told Reuters adding that the conservative estimate of amounts paid could actually be higher.

Bulgaria’s energy minister told Reuters she did not believe the Commission would find any problem.

“Until now we have not seen any obstruction, including from the European Commission,” Temenuzhka Petkova said.  

If the Commission finds aid has been given illegally, it can order the country to recover it.