For the second time in a month, the Trump administration has rolled back emissions restrictions on coal-fired power plants.

Early in December, the EPA announced a new proposal that would undo carbon-dioxide limits on coal plants, overturning one of President Obama's signature climate change programs, the Clean Power Plan, which never went into effect after a court injunction.

That plan would increase the allowable global warming emissions from coal-fired power plants by 35 percent over current law.

READ THIS: EPA rolls back emissions standards on coal plants

The latest proposal would also allow coal plants to emit more toxic mercury, which has been found to cause developmental disabilities in children and harm pregnant women.

The proposal, released Friday in the midst of a government shutdown and in the middle of the holiday break between Christmas and New Year's, doesn't set a specific new looser standard, but changes the formulas for cost-benefit calculations to make it easier to set looser emissions standards well into the future, according to a Reuters report.

In a statement releasing the new proposal, Acting EPA Administrator Andrew Wheeler said, "it is not ‘appropriate and necessary’ to regulate HAP (Hazardous Air Pollution) emissions from coal- and oil-fired power plants... because the costs of such regulation grossly outweigh the quantified HAP benefits.” Wheeler is a former coal industry lobbyist.

READ MORE: EPA plans to roll back emissions standards on power plants

The statement also said that some "unquantified benefits" of reduced healthcare costs from lower mercury emissions were not enough to justify the standards.

The proposal was released despite the fact that a coalition of electric utilities said the reduction is not necessary, because its members have already invested billions in new technology to comply with the old standards and cut mercury emissions.

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In a statement from the director of its Beyond Coal Campaign, Mary Anne Hitt, the Sierra Club said, "Virtually every coal plant in the U.S. has already met this lifesaving standard, and now Trump is recklessly trying to roll it back.... The policy Andrew Wheeler and Donald Trump proposed today means more pregnant women, young children, and the elderly will be exposed to deadly neurotoxins and poisons, just so wealthy coal and oil barons can make a few extra bucks."

Coal-fired electric power plants have been identified as the main source of mercury in U.S. air.

Cleaner electric power is a key ingredient in making electric cars useful in reducing overall air-quality and greenhouse-gas emissions.