WASHINGTON, April 15 (Reuters) - The Trump administration has exempted 47 companies from regulations to curb mercury and air toxics for their coal-fired power plants for two years, according to a list of facilities published by the Environmental Protection Agency on Tuesday.

The exemptions list is the latest move by the administration to use executive or emergency orders to immediately shield polluting facilities from compliance with air and water standards tightened by the Biden administration as the EPA undertakes a lengthier process to roll back those rules.

The Biden-era Mercury and Air Toxics Standard is still in force after the Supreme Court in October declined to put the rules on hold after a group of mostly Republican states and industry groups led a legal challenge to suspend it.

But U.S. President Donald Trump issued a proclamation last week detailing that certain stationary sources subject to MATS are exempt from compliance in a bid to revive the coal industry and prolong the life of aging coal power plants.

Coal-burning plants generate less than 20% of U.S. electricity, a drop from 50% in 2000, according to the Energy Information Administration, as fracking and other drilling techniques have hiked production of natural gas. Growth in solar and wind power has also cut coal use.

Mercury is a potent neurotoxin the American Lung Association says could cause severe developmental harm. Mercury and other air toxics associated with coal burning raise the risk of asthma attacks, strokes, heart attacks and lung cancer.

The Biden-era rule required constant monitoring of emissions.

Supporters of the exemption said the MATS rule placed severe burdens on coal-fired power plants and on the viability of the U.S. coal sector.

Montana Republican Congressman Troy Downing applauded the inclusion of two units of the Colstrip coal plant to the exemption list, adding that it "will provide clarity and certainty for operations going forward."