Czech trade watchdogs have fined a unit of German utility RWE a record $17m (£8.9m) for violating competition laws.
Regulators said RWE’s gas operation, Transgas, had discriminated against regional gas distributors by offering better deals to its own subsidiaries.
The Office of Fair trade also said Transgas had limited competition by banning its distributors from selling gas outside their territory.
The fine is the highest to be imposed on a single firm in the Czech Republic.
“The dominant company’s behaviour can be termed very serious, because it poses a very significant barrier for gas traders to develop their business in a sector undergoing liberalisation,” said Martin Pecina, chairman of the trade body.
An investigation by the watchdogs also found that the company – which imports Russian and Norwegian gas – had charged too much for gas storage.
RWE Transgas said it was surprised by the verdict, but added it hoped to find an “overall resolution of the situation”.
The group now has 15 days to appeal against the decision.