PITTSBURGH — U.S. Steel will invest more than $1 billion for state-of-the-art facilities in western Pennsylvania that it says will improve its steelmaking efficiency and reduce emissions at its Mon Valley Works operations, the company said Thursday.

The announcement comes just days after two environmental groups sued the steelmaker for violating the Clean Air Act.

U.S. Steel says new casting and rolling technology at its Edgar Thompson Plant will allow it to combine thin slab casting and hot rolled band production into one process, the first of its kind in the U.S. The steelmaker said Thursday that a new cogeneration system at its Clairton Plant will feature an emissions control system that can convert some of the coke oven gas generated there into electricity to power other parts of the plant.

PennEnvironment, one of the groups that sued U.S. Steel on Monday, alleged that the company operated plants at Mon Valley Works for three months without pollution control equipment. The group said the U.S. Steel plants south of Pittsburgh “showered residents with unlawful pollution,” including sulfur dioxide, a respiratory irritant.

A spokeswoman for U.S. Steel said the company doesn’t comment on active litigation.

U.S. Steel Corp., based in Pittsburgh, expects the first coil production from the new facility in 2022.

It’s the second major operational upgrade U.S. Steel has announced this year. In February, the company announced it was restarting construction on an idled manufacturing facility in Alabama, crediting President Donald Trump’s trade policies. U.S. Steel said Trump’s “strong trade actions” were partly responsible for the resumption of work at a plant near Birmingham. Trump imposed a 25% tariff on steel imports last year.