BILLINGS — Wildlife advocates went to federal court Tuesday to challenge a move by Congress that stripped endangered species status from more than 1,300 gray wolves across five states in the Northern Rockies.

The two-hour hearing before U.S. District Judge Donald Molloy in Missoula came as Idaho and Montana prepare for fall hunts in which hundreds of wolves could be killed.

A ruling is now pending. Courtroom observers said Molloy pledged Tuesday to quickly issue his order deciding the case.

Molloy has twice blocked prior attempts to lift protections for the predators. This time around, he is considering whether Congress violated the separation of powers under the U.S. Constitution with legislation crafted to circumvent his earlier rulings.

Congress approved a budget bill in April that contained a provision targeting wolves inserted by two Western lawmakers, Republican Rep. Mike Simpson of Idaho and Democratic Sen. Jon Tester of Montana.

Signed into law by President Barack Obama, the measure marked the first time since the passage of the Endangered Species Act in 1973 that Congress forcibly removed protections from a plant or animal.

Several conservation and environmental groups filed suit in May.

They said Congress crossed the divide that separates the branches of the federal government by getting involved in a pending legal case instead of sticking to its role of making law. The groups cited Tester's comments in media interviews during the budget bill debate that he was not amending the endangered act itself.

But Department of Justice Attorneys argued that is exactly what Congress did with the budget bill rider - change the law so wolves were left out of it.

"Congress acted well within its constitutional authority," the attorneys wrote in court filings. "Congress's power to modify the law, which in turn affects judicial decisions based on the old law, is well established."

Wolves also were taken off the endangered species list in Washington, Oregon and Utah, but no hunts are planned in those states, which combined have only a few dozen wolves.

About 350 wolves in Wyoming remain on the list due to concerns among federal officials over a law allowing the predators to be shot on site across most of the state. Secretary of Interior Ken Salazar has been negotiating a potential compromise with Wyoming Gov. Matt Mead but no deal has been announced yet.