Gov. Larry Hogan’s administration warned the Environmental Protection Agency on Thursday that it will sue if the federal agency does not stop coal-fired power plants in Indiana, Kentucky, Ohio, Pennsylvania and West Virginia from contributing pollution to Maryland’s air.

The warning letter follows an initial complaint filed in November.

The 19 power plants in upwind states already have the technology to control the amount of nitrogen oxides released into the air, according to state Secretary of the Environment Ben Grumbles, but they aren’t using it during the summer, when it’s needed most.

As a result, Maryland’s urban areas may not meet new, more stringent Clean Air Act requirements without reducing the smog from other states.

The pollution harms the Chesapeake Bay watershed, too, Grumbles said.

“Gov. Hogan has put a real emphasis on a holistic approach to preventing pollution, and that's not just upstream pollution along the Susquehanna River,” he said. “It's also air pollution coming in from power plants from the Midwest.”

Maryland is asking for fixes utilities here have already made, Grumbles said. He added that the changes would level the playing field for Maryland energy companies.

The Chesapeake Bay Foundation praised the administration for the move. In a statement, Vice President of Litigation Jon Mueller said the 19 power plants the state’s letter mentions earned an extra $24 million profit by not using its nitrogen oxide-controlling technology.