"Today we launched suits against four companies...Throughout the fourth quarter of 2008 they did not reduce retail fuel prices, while oil prices were falling," said Igor Artemyev, who heads the Federal Antimonopoly Service (FAS).
The four companies also hiked wholesale prices in January 2009, Artemyev added. He also called the oil companies' behavior a "challenge" to the Russian government.
"The challenge was issued, and we accepted it," he said.
Last summer, the FAS fined the four oil producers from 1.1 billion rubles ($31.6 million) to 1.5 billion rubles ($43 million) for abusing their monopoly positions on the market.
"Our new methods suggest fines will grow several fold," the FAS head warned on Tuesday.