Maine’s attorney general has a joined a multi-state lawsuit challenging the Trump administration’s decision to roll back new greenhouse gas emissions rules on power plants.

Attorney General Aaron Frey added Maine to the group of 21 other states and seven local governments that filed suit in the U.S. Court of Appeals in Washington, D.C., to protect Obama-era rules requiring power plants to reduce emissions of climate-altering gases. Under the Trump administration, the U.S. Environmental Protection Agency has proposed replacing the rules with regulations that would result in dramatically smaller reductions in emissions.

“Fossil-fueled power plants are major sources of climate change pollution,” Frey said in a statement. “Beyond the impacts that climate change itself has on Maine’s natural resources and economy, we also know that emissions – from these plants – including plants outside of Maine – pollute our air and water. Rolling back rules to limit this type of pollution violates the federal Clean Air Act, and will result in negative consequences for Mainers’ health, economic well-being, and way of life.”

This is just the latest in a string of lawsuits challenging President Obama’s controversial Clean Power Plan as well as the Trump administration’s attempts to undo one of his predecessor’s signature policies on climate change.

While the Obama-era rules would apply to all fossil fuel-fired power plants, they were aimed squarely at coal-fired plants that emit the largest amounts of greenhouse gases as well as other air pollutants. The rules have been hung up in the courts as attorneys general in Republican states and the coal industry sought to block their implementation.

The Clean Power Plan rules were not expected to have a major impact on Maine’s electricity generation sector because Maine already participates in a multi-state compact, known as the Regional Greenhouse Gas Initiative, that uses a cap-and-trade system to reduce power plants emissions. But Maine and other New England states expected to benefit by receiving less air pollution drifting into the region from coal-fired plants in other states.

In June, the Trump administration unveiled an alternative to the Clean Power Plan – dubbed the Affordable Clean Energy rule – that would focus more on encouraging installation of more efficient technology at power plants. The Trump administration has been accused of ignoring or silencing scientific warnings on climate change, and critics contend the new rules will do little to reduce emissions.

New York Attorney General Letitia James led the multi-state lawsuit filed Tuesday in Washington. The other states or cities involved in the lawsuit are California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maryland, Massachusetts, Michigan, Minnesota, New Jersey, New Mexico, North Carolina, Oregon, Pennsylvania, Rhode Island, Vermont, Virginia, Washington, Wisconsin. Those states were joined by the following cities: Washington, D.C., Chicago, Los Angeles, New York, Philadelphia, South Miami and Boulder, Colorado.