A federal court wants the Environmental Protection Agency (EPA) to report, with “precision and specificity,” how it plans to take a key step in implementing a 2015 smog pollution rule.

The demand from the Court of Appeals for the District of Columbia Circuit came after the EPA said in November which areas of the country comply with the regulation, but refused to say which areas do not comply.

Both kinds of designations were due Oct. 1, two years after the Obama administration finalized its major ground-level ozone rule. Environmentalists and Democratic states have sued the EPA to force the declarations known as “nonattainment” designations.

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The order late Tuesday from a three-judge panel of the federal court mandated that the EPA file a report by Jan. 12 “identifying with precision and specificity when it plans to file a final rule establishing air quality designations for the 2015 ozone national ambient air quality standards for those areas in the United States that remain undesignated.”

EPA Administrator Scott Pruitt Edward (Scott) Scott PruittJuan Williams: Swamp creature at the White House Science protections must be enforceable Conspicuous by their absence from the Republican Convention MORE opposed the regulation in his previous job as Oklahoma’s Republican attorney general and sued to stop it.

Earlier this year, Pruitt attempted to delay by one year the compliance designations. Facing lawsuits, he walked that back. But he still hasn’t said which areas don’t comply.

“In the spirit of cooperative federalism, EPA will continue to work with states and the public to help areas with underlying technical issues, disputed designations, and/or insufficient information,” the EPA said in November. “Additionally, EPA modeling, state agency comments, and peer-reviewed science indicate international emissions and background ozone can contribute significantly to areas meeting attainment thresholds. The agency intends to address these areas in a separate future action.”

In nonattainment areas, states must write plans to reduce ozone pollution. Since most ground-level ozone is a byproduct of burning fossil fuels, those plans would likely seek to restrict fossil fuel use.