ST. LOUIS, Mo. (AP) — The St. Louis-based electric utility Ameren Corp. said in a court filing Tuesday that it will close a coal plant several years early, a move that follows a court order this summer requiring pollution controls that would potentially cost hundreds of millions of dollars.

The plant sits along the Mississippi River near Festus, Missouri, about 40 miles  south of St. Louis. In August, the 8th U.S. Circuit Court of Appeals upheld a ruling in a decade-old lawsuit, ordering Ameren to install pollution control equipment.

The federal government argued that modifications in 2007 and 2010 without proper permits led to increased sulfur dioxide emissions because the plant could burn more coal. Sulfur dioxide is a byproduct of burning coal that can harm the respiratory system.

Ameren maintains that air quality monitors near Rush Island meet federal and state standards. Rush Island is among four coal plants it operates.

Ameren had previously planned to close Rush Island in 2039. The court filing didn’t give a specific closure date but said it would be before the March 2024 compliance date required by the court.

“The decision to accelerate the retirement of the Rush Island Energy Center comes after carefully considering our legal, operational, and regulatory alternatives, as well as the impact on customer costs and system reliability,” Ameren President and Chairman Marty Lyons said in a statement. ”We remain committed to reliable and affordable electric service for the benefit of our customers and communities, while reducing emissions and building on our longstanding commitment to environmental stewardship.”

Ameren announced in September 2020 that it planned to invest $8 billion in renewable projects during the next two decades, with a goal of reaching net-zero carbon emissions by 2050 across Missouri and Illinois.

Andy Knott of the Sierra Club urged Ameren to close the plant as soon as possible.

“The financial and health interests of Ameren’s customers is best served by the utility replacing any needed capacity with a combination of renewable energy, energy efficiency, and demand side response,” Knott said in a statement.

By JIM SALTER for the Associated Press