WASHINGTON, Dec 28 (Reuters) - The Trump administration on Friday said limits on mercury emissions from coal-fired power plants were no longer necessary as their costs outweighed the benefits, a move environmentalists said was favorable for the coal industry and could increase health hazards.

Under the Mercury and Air Toxic Standards, or MATS, enacted under former President Barack Obama, coal plants have been forced to install expensive equipment to cut output of mercury, which can harm pregnant women and put infants and children at risk of developmental problems.

Since August, the Environmental Protection Agency (EPA) has been reconsidering the justification for the rule.

Electric utilities have pushed back on the potential loosening of requirements, saying they have already invested in technology to cut emissions of the dangerous pollutant.

In a statement issued on Friday during a partial government shutdown, the EPA said the emission standards of the MATS rule would remain in place. But it proposed to withdraw the justification for the requirements.

“EPA is proposing that it is not ‘appropriate and necessary’ to regulate HAP emissions from coal- and oil-fired power plants... because the costs of such regulation grossly outweigh the quantified HAP benefits,” it said.

The industry had challenged a 2016 conclusion by Obama’s EPA that the rule was justified because savings to U.S. consumers on healthcare costs would exceed compliance costs. The calculations accounted for how pollution-control equipment would reduce emissions of other harmful substances in addition to mercury.

Since taking office in January 2017, Trump has targeted rolling back Obama-era environmental and climate protections to maximize production of domestic fossil fuels, including crude oil. U.S. oil production is the highest in the world, above Saudi Arabia and Russia, after a boom that was triggered more than a decade ago by improved drilling technology.