Topeka ? The federal government has filed a lawsuit accusing Westar Energy Inc. of violating federal air quality laws at one of its coal-fired power plants.

The federal lawsuit, filed Wednesday in Kansas City, Kan., says Westar made major modifications to the Jeffrey Energy Center in St. Marys over the past decade but didn’t update the plant’s pollution control equipment.

The lawsuit asks the court to force Topeka-based Westar, the state’s largest electric utility, to install the new equipment and potentially pay millions of dollars in fines.

Attorneys for the Justice Department and the Environmental Protection Agency claim that the upgrades are required whenever a utility makes significant changes to a power plant.

Without those upgrades, the lawsuit says, the plant may produce higher levels of such pollutants as sulfur dioxide, nitrogen oxide and particulate matter, which can contribute to smog and acid rain.

Westar also operates the Lawrence Energy Center, a coal-fired power plant north of the city.

In a release, Westar defended its record, saying it has invested almost $500 million in recent years to cut its emissions and plans to invest another $1 billion over the next five years.

“We are good environmental stewards,” the company wrote.

Westar also said the plant modifications were made 10 to 15 years ago when it was believed the modifications complied with federal environmental law.

The Justice Department said the case is part of a national effort to force operators of coal-fired power plants to reduce pollution.

On Tuesday, Kentucky Utilities agreed to settle a similar lawsuit by installing $135 million in upgrades to a central Kentucky power plant and paying $1.4 million in fines. The EPA said the modifications at the E.W. Brown Generating Station in Mercer County would reduce combined emissions of sulfur dioxide and nitrogen dioxides by more than 31,000 tons a year.