A Middle Island pet rescue under investigation by the state attorney general’s office was hit with a class-action lawsuit Monday claiming that sick dogs are being put up for adoption and fake pet medications are being distributed.

Miller Place attorney Vesselin Mitev said in a telephone interview that he filed the suit against Friends of Freddie Pet Rescue in Suffolk County Supreme Court Monday morning on behalf of himself and three other Long Islanders.

Mitev said they adopted their dogs there and soon afterward found them to have illnesses and problems ranging from pneumonia to parasites. One of their animals died, according to the lawsuit.

A representative from Friends of Freddie was not immediately available for comment Monday.

Mitev, who himself is a plaintiff, and adopted his Lab mix, Percival, from Friends of Freddie, said in the lawsuit that the Middle Country Road facility is a “public nuisance” that should be closed because some of the health problems are contagious.

The lawsuit claims that to “induce” adoptions, prospective “parents” were provided phony preventive medications to guard against certain health issues. Mitev said that when Percival came down with a cough, Mitev was given purported medicine by workers at the facility that he learned through his vet was actually a mixture of herbs and water.

Another plaintiff, Kenneth Harsch Jr., 28, of Medford, said in a telephone interview Monday that he adopted his Chiweenie — a Chihuahua-Daschund mix — around Thanksgiving of last year when the dog was 6 months old.

“When I got him home he was coughing and would have to lay down a lot,” Harsch said. He said he got the same medication from the facility and added, “My vet didn’t even know what it was.”

Harsch said the dog was diagnosed by the vet with advanced pneumonia, kennel cough and parasites.

Unspecified damages are being sought in the lawsuit, and Mitev said he is seeking out others who have had problems with the facility to join the legal action.

Friends of Freddie Rescue also is the subject of an investigation by the state Attorney General’s office, and a spokeswoman for the office said on Monday the probe was still ongoing. She has declined to provide information about the nature of the investigation or when it started.

Two of the plaintiffs in the lawsuit — Kristen Addiss, 27, of Port Jefferson, and Kim Kondak, 39, of Shirley — said in interviews with Newsday last week that they had reported to the attorney general’s office their experience with sick dogs they adopted from the rescue.

After the attorney general’s investigation was revealed last week, Beth Matthews, a volunteer at Friends of Freddie, said she was aware of the probe but said it had to do with paperwork and questions about whether the facility has kept proper records as a nonprofit operation.

Matthews, who said there were about 70 dogs being housed at the shelter as of last week, acknowledged there had been complaints of sick animals but she said that comes with taking in rescue dogs that could come from across the country. She said they can appear healthy and have an illnesses develop weeks later. She said it was also possible some of the new owners did not take care of their dogs properly after they left the shelter.