Motivated by what it calls acts of cruelty in poultry slaughterhouses, the Humane Society of the United States says it will file suit today seeking to extend federal controls over livestock slaughter to protect birds.

The federal suit against the U.S. Agriculture Department will challenge the exclusion of poultry from the Humane Methods of Slaughter Act, which requires that livestock be rendered unconscious or killed before being butchered.

The suit, to be filed today in U.S. District Court in San Francisco by the Humane Society and other animal rights advocates contends that the most widely used method of poultry slaughter injures still-conscious birds and results in an increased chance of food-borne infections in humans, in part because the birds ingest feces during processing.

"The USDA's arbitrary decision to exclude 95 percent of the animals being slaughtered every year is causing needless suffering by these animals and increasing the risk to consumers, as well," said Paul Shapiro, Washington-based manager of the Humane Society's factory farming campaign. "Because of the USDA's failure to recognize that poultry are livestock, more than 9 billion birds are being slaughtered inhumanely every single year."

Poultry farming is a key to the economy in communities just beyond the Washington area: Eastern Shore farms in Maryland, Virginia and Delaware generate about $1.7 billion annually, and those in Virginia's Shenandoah Valley bring in $615 million.

In most plants, live birds are hung upside down on an overhead conveyor, and their heads run through electrified water to stun them before a machine slits their throats, the suit states.

The Humane Society's suit, joined by an Oakland, Calif.-based advocacy group and several individuals, contends that birds are injured by the conveyor's metal shackles and that they often are not knocked out by the stun bath. Further, the suit contends, live poultry that enter the stun bath or a scalding tank later in the process defecate and inhale feces suspended in the water, potentially contaminating the meat. The Humane Society advocates gassing birds, either killing or stunning them, before they go on the processing line.

The suit cites 2004 reports of a Pilgrim's Pride processing plant in Moorefield, W.Va., in which an animal rights advocate videotaped workers stomping on, kicking and throwing live chickens against a plant wall. Several workers were fired, but none were prosecuted, in part because the federal regulations do not apply to poultry, Shapiro said.

In a news release about its suit, the Humane Society also mentions a Perdue Farms Inc. chicken plant in Showell, on Maryland's Eastern Shore, in which animal rights workers documented last year what they said were instances of cruelty, including birds that should have been dead flapping their wings on processing lines.

The Salisbury, Md.-based company disputed the allegations. "We have a documented and audited poultry welfare program that ensures the birds in our care are treated humanely," as well as worker training to ensure proper handling, said Perdue spokeswoman Julie DeYoung. DeYoung said that after the videotape of the Showell plant -- now closed for reasons unrelated to the allegations -- was released, procedures there were "thoroughly investigated, and we did retrain employees."

In a news release, Perdue quoted a company veterinarian who said the wing-flapping in the video was "an involuntary muscle reaction that normally occurs after death."

USDA spokesman Steven Cohen said the agency would not comment on the suit until it is filed.

Although there is no specific humane handling and slaughter law for poultry, he said, inspectors and veterinarians stationed in every poultry processing plant "monitor production so if a plant has evidence of excessive bruising or other conditions that would indicate handling in a manner inconsistent with humane handling, we would necessarily look into that operation."