The Supreme Court has refused to block a Biden administration rule aimed at preventing legacy toxic waste from closed coal plants from seeping into and contaminating nearby groundwater.

In a brief order, the court denied an emergency request from the East Kentucky Power Cooperative to temporarily halt the rule while ongoing litigation challenging it is resolved, The Hill reported.

The Supreme Court did not provide an explanation for its decision to reject the power cooperative’s petition, and no dissents were noted, the outlet said.

The ruling does not necessarily indicate that the justices believe the rule is lawful; it simply means they are not prepared to block it before lower courts have ruled on the challenges.

The rule in question targets “coal ash,” a byproduct of coal plants containing hazardous substances such as mercury and arsenic. It mandates that coal plants closed before October 19, 2015, take measures to prevent coal ash from leaking out of storage ponds.

The East Kentucky co-op asked the court to halt the rule, arguing that it would suffer from “unrecoverable compliance costs” if it did not.

Earlier this week, the nation’s highest court passed up an opportunity to correct a ruling by Hawaii’s Supreme Court that appears to violate Second Amendment interpretations.