Seven Democratic states on Friday threatened to sue the Trump administration for its delay in enforcing an Obama administration rule on air pollution from landfills.

The Environmental Protection Agency (EPA) was supposed to, by Nov. 30, approve state plans to comply with the 2016 landfill methane rule or impose federal compliance plans on states that do not comply.

But the agency did not complete that step of the process, which the states say is a violation of the EPA’s responsibilities under the Clean Air Act.

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“Climate change is the most important global environmental issue of our time. We must act to address it now for the sake of our children,” California Attorney General Xavier Becerra Xavier BecerraOVERNIGHT ENERGY: Trump casts doubt on climate change science during briefing on wildfires | Biden attacks Trump's climate record amid Western wildfires, lays out his plan | 20 states sue EPA over methane emissions standards rollback 20 states sue EPA over methane emissions standards rollback Investigation underway after bags of mail found dumped in Los Angeles-area parking lot MORE (D), who is leading the effort, said in a statement.

“EPA Administrator [Scott] Pruitt has a legal responsibility to enforce this critical landfill methane regulation. If he fails to do his job, our coalition is ready to go to court.”

The states are obligated under the Clean Air Act to file notice 60 days before they can file a lawsuit.

The EPA did not respond to a request for comment.

Blue states have filed dozens of lawsuits or other challenges against the Trump administration, including many on environmental or energy policy issues. In the environmental arena, Becerra alone has achieved nine legal victories and has not lost any case.

The 2016 landfill rule was meant to reduce the output of methane from landfills. Decomposition creates methane, a greenhouse gas that is at least 80 percent more potent than carbon dioxide.

The rule was part of an administration-wide crackdown on methane emissions under former President Obama. But it faced opposition from industry and Republicans, who complained that it was too costly to implement.

In May, Pruitt said he would reconsider the regulation and put a 90-day halt on its implementation. But that halt didn’t explicitly change the deadlines for states or the EPA to take action.

Pruitt still hasn’t said what, if any, parts of the rule he’s interested in changing and hasn’t indicated if he has finished the reconsideration process.