(Reuters) -The U.S. Supreme Court turned away on Monday Exxon Mobil Corp's bid to overturn a $14.25 million civil penalty that a judge imposed in a long-running lawsuit over air pollution at its Baytown, Texas, crude oil refinery.

Exxon had asked the justices to take up the case after a lower court in December upheld the largest penalty ever assessed in a citizen-initiated lawsuit enforcing protections against air pollution under the landmark Clean Air Act environmental law.

The lawsuit, filed in 2010 by the Environment Texas Citizen Lobby and the Sierra Club, focused on Exxon's operation in Baytown of the largest petroleum and petrochemical complex in the United States.

The plaintiffs said that the facility routinely exceeded limits under the Clean Air Act on emissions of harmful air pollutants, affecting the daily lives and health of people who live and work nearby by emitting toxic, carcinogenic and ozone-forming chemicals.

Houston-based U.S. District Judge David Hittner in 2017 issued a $19.95 million penalty to Exxon, finding it was responsible for the pollution from the Baytown complex between 2005 and 2013.

The New Orleans-based 5th U.S. Circuit Court of Appeals later threw out the penalty and ordered Hittner to reassess it, resulting in the judge in 2021 issuing a new $14.25 million penalty, which the appellate court ultimately upheld.

On appeal to the Supreme Court, Exxon argued that the plaintiffs lacked legal standing to pursue the case and that the 5th Circuit, like some other federal appeals courts, had adopted a novel standard to assess standing that the justices should reject.

Exxon said that under the 5th Circuit's standard, plaintiffs in environmental cases seeking penalties for Clean Air Act violations may establish standing simply by showing that the injuries they suffered are the kinds that a defendant's conduct could have caused, rather than likely caused.

Exxon urged the Supreme Court to use the case as means to overturn its 2000 ruling in the case called Friends of the Earth v. Laidlaw Environmental Services Act, which held that citizens may have standing to seek penalties under the Clean Air Act even though any penalties are paid not to them but to the U.S. Treasury.

The Supreme Court has a 6-3 conservative majority, and its ideological makeup has shifted to the right since that case was decided in a 7-2 ruling.

The only currently sitting justice to participate in that case, conservative Justice Clarence Thomas, joined a dissenting opinion by the late Justice Antonin Scalia, who wrote that the case was decided on "preposterous" grounds.