MONROE, N.C. -- A lawsuit filed in Monroe on Friday asks a judge to stop Union County's animal shelter from killing young, geriatric, injured, sick or pregnant animals in its gas chamber.

“We hope to stop the inhumane euthanasia of defenseless animals,” said Sue Ratliff, head of the Humane Society of Union County.

Her group and another, the North Carolina Coalition for Humane Euthanasia, are suing Union County. They support lethal injections for euthanasia. Their attorney, Rodney Alexander, said many of the deaths in Union County's gas chamber violate state law.

“Union County's sheriff's department, based on documents we've received from them, is euthanizing young, sick, injured, old and pregnant animals in the gas chamber,” Alexander said. “We believe that it's against the law.”

The lawsuit points to a state law that says counties must follow methods approved by three specific animal groups: the American Veterinary Medical Association, the Humane Society of the United States and the American Humane Association.

All three of the groups mentioned in the lawsuit say they prefer that animals shelters use lethal injection, and they also have concerns about using the gas chamber for animals that are very young, very old, sick or pregnant.

The organizations claim that because those animals have lungs that don't work as well, it takes too long for the poison to kill them humanely.

Animal rights groups analyzed hundreds of records obtained from Union County, which they say document violations of state law. They cite dozens of examples, including a 2-week-old kitten, a dog that was old, blind and sick and injured and pregnant cats. In each case, the county's documents list the cause of death as “chamber.”

On Friday workers inside the shelter couldn't explain the documents but said they don't put young, old or pregnant animals in their gas chamber, and Union County Sheriff Eddie Cathey denies his department is doing anything wrong.

Cathey said, “We're aware of state law and we're complying with it.”

“If there's evidence we're not complying with state law, it'd be a surprise to me,” he said.

Cathey said he agrees that young, old and sick animals shouldn't be put in the gas chamber. But so far, he can't explain why so many animal shelter records seem to suggest that it's happening.

He said he'll have more to say once he's had a chance to take a close look at what's in the lawsuit.

The suit could go to court within 60 days.