An animal rights group is pursuing criminal charges against Tyson Foods and six of the company's employees after undercover video footage from a Mississippi slaughterhouse allegedly showed workers punching and throwing chickens before killing the birds.

In September, the group Mercy For Animals sent an operative outfitted with a hidden camera to work at a Tyson poultry plant in Carthage, Mississippi. The resulting footage, released on Wednesday, purportedly caught workers "punching, throwing, beating, pushing, and otherwise tormenting frightened animals for fun." The activist group also claims workers were seen shocking and decapitating birds.

"The workers were dumping the chickens on top of each other, causing them to suffocate to death," Mercy For Animals spokesman Matt Rice said.

The undercover worker allegedly reported the abuses to his supervisors and called a corporate hotline, but Mercy for Animals says there were no repercussions or changes to the way chickens were handled at the plant.

Tyson Foods released a statement on Wednesday that said the company has been investigating the abuses since they received a complaint last week, and that two workers shown in the video have already been fired.

"We believe proper animal handling is an important moral and ethical obligation," the company said. "Everyone who works with live animals in our plants — including the person who secretly shot this video — is trained in proper animal handling and instructed to immediately report anything they believe is inappropriate."

Tyson also pointed out that authorities have not filed criminal charges against the company or its workers. Mississippi allows citizens to file criminal charges against other individuals, however, and Mercy for Animals has filed 33 animal cruelty charges in connection with its investigation. A judge will review the case for probable cause and decide whether to issue arrest warrants.

Mercy For Animals posted the video of the abuses, narrated by the actress Candice Bergen, on its website with a link to a petition calling on Tyson to change its animal protection practices.

This is the third sting operation by the group against Tyson since July, with at least one case resulting in criminal charges against the owners of a poultry farm, Rice said.

The larger point, according to Rice, is that chickens are the most widely-abused animal in the country and receive no protections from the federal Humane Methods for Slaughter Act despite accounting for about 95 percent of the animals killed for food in the US.

The activist group would like to see Tyson implement more humane slaughter methods. Specifically, they want a "controlled atmosphere system," in which the chickens arrive at a slaughterhouse and are put in a room with inert gases added to the air to put the birds to sleep before they are killed, removing the human aspect of subduing and killing the birds.

Rice speculated that workers become "desensitized" because of the speed and volume of killing the job requires. The facility in Carthage processes some 2.5 million chickens a week, he said. He likened the mentality of slaughterhouse workers to that of soldiers who are taught to hate the enemy so they can do their jobs.

"If you talk to the workers they will tell you they have to learn to hate the animals to go to work every single day," he said. "We'd like to eliminate need for workers to handle live birds at all, which would prevent them from maliciously torturing animals."

Tyson is the largest chicken supplier in the United States, providing poultry to a number of major national food chains, including McDonald's. Rice said that his group's previous undercover investigations have helped lead to corporate policy changes at Nestle and Walmart, and they hope Tyson will begin to consider changes next.