Russian coal miner Raspadskaya declared force-majeure following a mine blast that killed at least 66 miners earlier this month.
The force-majeure notice will allow Raspadskaya to stop or drop volumes under contracts without paying fines due to unavoidable circumstances.
The notice was sent to Russian and foreign metal and coke-chemical companies, and transportation enterprises and ports.
Production at its two unaffected units will only be 350kt per month and coal concentrate sales will be 255kt a month from June 2010 for the following three to four months, Raspadskaya said.
The combined output of three units before the blasts amounted to 950kt per month while coal concentrate sales were 760kt a month.
Russian prosecutors earlier said they would probe safety at all Russian coal mines.
The general director of the Raspadskaya mine has been charged with criminal negligence in relation to two methane gas explosions that rocked the mine on 8 May, killing 90 miners.