The RSPCA says it has serious concerns about the treatment of pigs shown in footage recorded by an animal welfare group at two Norfolk farms.
The Animal Equality action group has produced images of pigs being kicked and hit at the East Anglian Pig (EAP) Company, based near Norwich.
The EAP is approved by the RSPCA's Freedom Food and works within the Red Tractor Assurance Scheme.
Both farms were visited by the RSPCA last week.
Animal Equality said the footage was recorded by an undercover investigator at two of the farms managed by the company; Little Thorns weaner unit near Swaffham and The Piggery at Didlington.
The images, seen by the BBC, appear to show pigs in overcrowded stalls and a lame pig is seen with a twine muzzle over its snout.
Andrew Knight, a vet speaking on behalf of Animal Equality, said the images showed pigs with large tumours as well as new-born piglets struggling to breathe.
"No reasonable person could fail to be appalled and disgusted by the cruel and callous treatment frequently endured by these highly-intelligent, sensitive animals," he said.
"The public would be shocked if it knew the truth about the conditions in which these pigs were raised."
A spokesman for the EAP said it was carrying out a full internal investigation into the handling of livestock.
But the company said the RSPCA had visited both farms involved in the investigation last week and given each a "clean bill of health".
"We totally condemn and do not tolerate any animal mistreatment or malpractice and operate in accordance with Freedom Food, Red Tractor Assurance Scheme and the Pig Veterinary Society policies and guidelines," the spokesman said.
"The RSPCA has confirmed there are no grounds for prosecution and are engaged in further meetings with the company during this week."
The EAP is approved by the RSPCA's Freedom Food welfare scheme, in which members are inspected by a trained assessor once a year.
A spokeswoman for the RSPCA said an inspector had visited the site at Didlington on Thursday, as soon as the charity was made aware of the footage.
The charity had decided the best way to address concerns was to work with the company and the RSPCA would not be prosecuting the firm, she said.
"We have serious concerns at some of what is shown in the footage taken by Animal Equality," she said.
"We believe that some of the sick pigs shown in the footage should also have been culled and there was evidence of poor practice when trying to remove an abscess from a sow.
"We're also very concerned that a sick sow appeared to have been left in an open area with twine tied around the jaw, but with no evidence that immediate culling was about to take place.
"This clearly requires further investigation of the circumstances."
The spokeswoman said an urgent meeting had been planned with the management of the East Anglian Pig Company, at which RSPCA inspectors would set out "changes that need to be implemented with the utmost urgency to address our concerns".