Two animal welfare groups filed a petition Tuesday with the U.S. Department of Agriculture outlining arguments for why they believe the department is legally obligated to establish rules in poultry plants that prohibit animal abuse and set clear penalties for violators.

Chickens and turkeys are not currently covered by the Humane Methods of Slaughter Act, and for decades animal welfare groups have fought unsuccessfully to have them included. Cattle, swine and most mammals have clear legal protections against abusive treatment in slaughterhouses.

However, under terms of the Poultry Products Inspection Act, plants may be cited if mistreatment of a bird causes some or all of it to become unfit for human consumption. In the mid-2000s, following a series of undercover videos by People for the Ethical Treatment of Animals, the USDA issued guidelines, instructing its inspectors to cite plants when such abuse was spotted. Formal rules, however, were not adopted.

“A rule is a legal obligation,” said Bruce Friedrich, senior policy director for Farm Sanctuary. “Until you have a rule, you can’t get meaningful enforcement. This next step is needed.”

Enforcement documents from January 2011 to July 2012, obtained by the Animal Welfare Institute and Farm Sanctuary, show USDA inspectors cited less than half of poultry plants for such violations under the current guidelines. The animal welfare groups say this is evidence that enforcement is hit or miss. The documents also show that when USDA inspectors did cite plants, they referenced animal welfare standards set by the poultry industry, not standards set by the department itself.

“There is little basis in the current regulations for what they are doing,” said Dena Jones, Farm Animal Program Manager at the Animal Welfare Institute. “This is probably one of the reasons why we are seeing so few plants being cited.”

USDA spokeswoman Catherine Cochran said the department “looks forward to reviewing the petition.” She declined to provide further comment.

Federal law requires that the agency’s response to the petition be “timely,” but there is no set deadline. If the USDA decides to move forward with writing proposed regulations, it would first post them and then review comments they receive from the industry, animal welfare groups and the public before proposing final regulations. The process, on average, takes two years.

The National Chicken Council, a trade group that represents the industry, said in a written response to the petition that it believes animal abuse is “exceedingly rare” and that the necessary guidelines and directives are already in place to deal with problems when they arise.

The group also said that USDA does not have the authority to regulate issues “that do not affect food safety, wholesomeness or labeling; and contrary to its allegations, nowhere in this petition is there a genuine link between humane handling of chicken and food safety.”

In October, a Washington Post article detailed problems with abuse in poultry plants, including how nearly 1 million birds are boiled alive each year in slaughterhouses, often because fast-moving lines failed to kill the bird before they are dropped into scalding water that helps defeather them. The article also quoted USDA inspectors and cited department documents that showed live birds frequently suffer broken bones when harried workers flip them upside down and force them into metal shackles.

Animal welfare groups are concerned that such abuses will increase under  a new inspection system being proposed by the department that would allow poultry companies to accelerate their processing lines by 25 percent. The department says the new system will help remove pathogens from the food supply and make plants more efficient.

“We would hate to see the slaughter inspection rules go through without humane handling regulations being adopted first,” Jones said. “If the line speeds are allowed to go faster without these rules being in place, animal suffering will also rise.”