Of the 38 proceedings, 12 were started last year.

The largest single fine so far - of €7.5 million - was issued in December 2015 to EDP Comercial, the free-market unit of Energias de Portugal, for offences relating to the application of lower electricity tariffs for less well-off consumers. The company has contested the finding.

In a statement on Wednesday, the ERSE said that infraction proceedings have been started against various companies in the electricity and gas markets, on the basis of the violation of their statutory duties.

As well as failures to attribute lower-rate tariffs, offences included the illicit ceding of natural gas to third parties, the failure to provide a full breakdown on bills, as well as unduly cutting off energy supplies.

There are 18 proceedings currently underway, according to the ERSE.