GREENVILLE, S.C. -- A national pet store chain is under fire tonight accused of selling puppies that come from "puppy mills."

The Humane Society of the United States says Petland, which has hundreds of stores nationwide including a store in Greenville, sells puppy-mill puppies to unsuspecting customers.

The Humane Society conducted an eight-month investigation into the nation's largest retailer of puppies. They put together a video that they say shows the deplorable conditions at the puppy mills they say provide the animals that Petland stores sell.

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To see the HSUS video, click here

StopPuppyMills.org

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At a news conference on Thursday, Michael Markarian, with HSUS, said, "Our investigators over the course of eight months found that many Petland stores are marketing puppy mill puppies to unsuspecting shoppers."

Officials tracked the sale of nearly 17,000 puppies to Petland stores and found nearly all of them came from puppy mills in the Midwest.

Petland storeowners deny the claim and the chain's management said they spot-check breeders across the county to be sure they are reputable. . The only Petland store in South Carolina is located on Woodruff Road in Greenville.

In an e-mail response to the allegations, store owner Donnie Presley said, "Healthy, happy, well-socialized pets are our No. 1 priority as they have been for 10 years. We do not support substandard breeding facilities. This is sensationalism at its best."

Kim Pittman, of the Greenville Humane Society -- which has no connection to the Humane Society of the U.S. says consumers need to ask questions and be shown proof that any puppy they're considering buying doesn't come from a puppy mill.

Pittman says the conditions at puppy mills are horrible: "Cages upon cages, stacked up -- little room for the animals to turn around in -- animals that are sitting in their fecal matter."

She said, "So as a prospective buyer, you should be asking the store where these are coming from. Anybody that can't tell you that, they're in it for the money only."

The Humane Society of the United States Thursday urged Petland corporate officials to join Petsmart and Petco in adopting Humane Society animals only.