Gazprom and SUEK signed a letter of intent to form a joint venture earlier this month. The natural gas monopoly will control 50% plus one share in the new company, and SUEK will hold 50% minus one share.
"I, for one, am against the deal," Igor Artemyev said. "It is monopolization, pure and simple."
He said Gazprom has no coal assets, but as a result of the deal will expand its dominant position not only on the natural gas market but also the coal market in Siberia, the Urals and Russia's Far East.
"Therefore the anti-monopoly service will do all it can to bring this home to the government," he said.
Gazprom said previously that more coal should be used to generate electricity, while SUEK CEO Vladimir Rashevsky said the effective use of coal in the power generating sector will help meet the existing power shortage.
But Russia's economic development and trade minister said Gazprom's control of enterprises unrelated to the natural gas sector endangers the country's economy.
"With a total of $300 billion in assets, Gazprom's role in the economy will resemble state monopoly capitalism of the 19th century. This will throw the country back," German Gref said.
Gazprom holds significant non-core assets, including in agricultural enterprises, banks, financial companies, media and sport clubs.
