At a conference on metallurgy on Thursday, Vladimir Putin asked the Federal Antimonopoly Service (FAS) and the country's top prosecutors to pay special attention to the company, which sold commodities abroad at prices twice as low as domestic and global ones in the first quarter of 2008.
The Russian premier's criticism sparked the fall in the company's American Depository Receipts.
Mechel CEO Igor Zyuzin was admitted to a Moscow cardiology clinic Wednesday, a medical source said, and was unable to attend the conference.
The stock of other Russian ferrous metals producers fell on the London Stock Exchange, where a lot of Russian metals are listed, following the news on Thursday.
Metals companies listed on Russia's RTS and MICEX stock exchanges lost more than 5% on Friday morning.
"The market is expecting Mechel to offer an official explanation of the situation," which should prevent the shares from falling further, said Yekaterina Akhanova, director for investment and banking services at the Metropol investment company.
Mechel has several metal plants in Russia, Romania and Lithuania. It unites producers of coal, ore, nickel, steel and highly-processed steel products for domestic and foreign markets.
In 2007, the company's output totaled 21.2 million metric tons of coal and 5.1 million tons of rolled products.
The FAS, Russia's antimonopoly regulator, has already launched an investigation into the company.
A Mechel source said the company was surprised by Putin's criticism and that it was continuing normal operations.
The source said the prime minister's tone and criticism of Zyuzin were most "depressing," but the situation in the company remained calm.
