A federal appeals court has ruled against the Interior Department’s 2011 decision to delist the gray wolf under the Endangered Species Act.

The Court of Appeals for the District of Columbia ruled that Fish and Wildlife Service (FWS) regulators failed in their analysis of the act when they decide to remove protections for the gray wolf in nine states.

Interior “failed to reasonably analyze or consider two significant aspects of the rule — the impacts of partial delisting and of historical range loss on the already-listed species,” the court ruled on Tuesday. Judges vacated the decision, restoring protections for the wolves.

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Regulators in 2011 delisted the gray wolf in Minnesota, Wisconsin and Michigan and parts of North Dakota, South Dakota, Iowa, Illinois, Indiana and Ohio, arguing that the populations there were “significant” and that disease and humans did not pose a threat to the wolves.

The Humane Society of the United States (HSUS) sued over the decision, and in 2014 a federal district court ruled against the delisting effort.

Congressional Republicans and some Democrats are currently working on legislation to force the FWS to again delist the Great Lakes gray wolf and make sure the courts cannot undo the decision.

The Senate Environment and Public Works Committee passed the Hunting Heritage and Environmental Legacy Preservation for Wildlife Act last week with a provision that would delist the wolf and prohibit judicial review.

The House’s appropriations bill for the Interior Department has a similar provision, as does a separate bill from Rep. Collin Peterson (D-Minn.), neither of which has gotten a full House vote yet.

“A federal appeals court has recognized that the basis for the delisting decision was flawed,” said Jonathan Lovvorn HSUS’s senior vice president and chief counsel for animal protection litigation.”

"Congress should respect the ruling relating to the management of wolves in the Great Lakes and allow the Fish and Wildlife Service to re-examine the broader conservation questions raised by the courts.”

—Timothy Cama contributed. Updated at 1:22 p.m.