A coal-burning plant in Conesville, Ohio. (Michael S. Williamson/WASHINGTON POST)

Maryland is suing the U.S. Environmental Protection Agency in an attempt to force federal regulators to crack down on upwind air pollution from five other states.

Gov. Larry Hogan (R) requested the legal action on Wednesday, and state Attorney General Brian E. Frosh (D) filed a lawsuit with the U.S. District Court in Baltimore hours later.

Maryland officials claim that power plants in Indiana, Kentucky, Ohio, Pennsylvania and West Virginia are violating a "good-neighbor provision" of the U.S. Clean Air Act by not using their pollution-control technology daily during the summer months, when heat and sunshine speed up creation of ozone gases.

Seventy percent of Maryland's ozone pollution comes from upwind regions outside the state, Maryland officials say, contributing to respiratory illness and heart disease, and interfering with Maryland's ability to meet federal air-quality standards.

"Maryland has made significant progress in improving our air quality in recent years, and that progress is in jeopardy due to a lack of action by the EPA," Hogan said in a statement.

Under federal regulations, coal plants must install technology to remove pollutants such as sulfur dioxide and nitrogen oxides from their exhausts. But they don't have to use those systems continuously as long as average output meets federal standards.

Since 2015, Maryland has required its power plants to use such "scrubbing" systems daily during summer months. State officials want the EPA to impose similar requirements for upwind regions in other states.

Maryland asked federal regulators in November to force Indiana, Kentucky, Ohio, Pennsylvania and West Virginia to take steps reduce air pollution. State Secretary of the Environment Ben H. Grumbles notified the EPA in July of plans to sue the agency if it did not answer his department's request.

"This common-sense approach — running the pollution controls that are already installed but are not always being used in out-of-state power plants — is one of the smartest ways we can protect our citizens' lungs and level the playing field for businesses," Grumbles said in a statement.

Aside from its strict power-plant regulations, Maryland has also implemented some of the nation's most stringent vehicle-emissions standards.

Despite those efforts, the state is failing to meet federal ozone standards in three regions, according to the EPA's website. Those regions are Baltimore, the Washington suburbs and the northeast section of the state, which borders Pennsylvania and Delaware.

"It gets pretty hard after you attack those two sources of air pollution to find other ways of making the air cleaner and healthier," Frosh said in an interview. "The reason we're not succeeding is that the air coming out of other states is so polluted."

The EPA lawsuit is the latest in a string of legal actions the state has taken against the Trump administration.

Frosh, using authority the state legislature granted him this year to sue the federal government without the governor's permission, has joined more than half a dozen other lawsuits against the administration.

They include legal challenges to block Trump's initial travel ban; prevent the administration from cutting off federal cost-sharing subsidies for the Affordable Care Act; stop the administration from rolling back the Obama-era program that provides deportation protections for undocumented immigrants brought to the United States as children; and alleging that the president violated the Constitution's anti-corruption clause by accepting payments from foreign governments after taking office in January.