Two environmental groups asked a federal court on Thursday to verify that U.S. Steel violated air pollution regulations thousands of times at its Pittsburgh area plants, as part of a 2019 lawsuit against the company.

The suit stems from a fire on Christmas eve in 2018 at U.S. Steel’s Clairton Coke plant that knocked out pollution controls. For three months following the incident, the company operated its Mon Valley Works without that equipment.

U.S. Steel violated the Clean Air Act more than 12,000 times in 2018 and 2019, according to the lawsuit filed by PennEnvironment and Clean Air Council in the U.S. District Court for the Western District of Pennsylvania. They are now asking for what is called a summary judgment to verify that as a fact in the case.

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