U.S. Mine Safety and Health Administration said Monday that it will have mine inspectors "beef up" the enforcement of ventilation rules in response to Congressional testimony on a fatal blast at a Massey Energy Co. (MEE) mine in April.

The federal mine-safety agency said inspectors have been instructed to increase enforcement efforts. The agency is also issuing new bulletins to mine operators, reminding them of rules on mine ventilation, the operation of ventilation systems and the maintenance of methane monitors.

"These standards are not voluntary, and every mine operator in the country is on notice that (the agency) will not tolerate violations of ventilation standards," Joseph Main, assistant secretary of labor for mine safety and health, said in a statement.

The agency said the actions stem from testimony in May before the House Education and Labor Committee that raised questions about whether Massey Energy properly followed ventilation rules at the Upper Big Branch in West Virginia mine prior to the explosion that killed 29 workers.

The MSHA and Massey have clashed since the explosion over the ventilation system at the mine, with the company criticizing existing rules and saying the agency required changes that reduced air flow in the mine.

Shares of Massey Energy recently traded 28 cents higher to $31.70.

-By Mark Peters, Dow Jones Newswires; 212-416-2457; mark.peters@dowjones.com