WASHINGTON  The Humane Society of the United States sued the Agriculture Department on Wednesday for creating a “loophole” that it said is permitting potentially sick cows into the food supply.

The lawsuit, filed in federal court in Washington, accused the department of violating procedural requirements when it created the provision, giving the meat industry a financial incentive to send unhealthy cattle to slaughter. As evidence, the Humane Society cited its widely publicized undercover videotape of workers at the Westland/Hallmark Meat Company in Chino, Calif., abusing cows that appeared unable to walk.

Jonathan R. Lovvorn, a lawyer for the Humane Society, said that when the agency weakened the ban last year, it “did so without really telling people that that’s what they were going to do and without explaining how this complies with their obligation to protect consumers and ensure humane treatment.”

The lawsuit is likely to fuel tensions between the Humane Society and the Agriculture Department that have been growing since the video was publicly released in late January. The release led to the biggest beef recall in history, 143 million pounds, more than a third of which had been shipped to federal nutrition programs like school lunches.