Last summer in Iowa, a woman gave Hillary Clinton a mission for her presidency: Shut down the nation’s puppy mills, commercial dog breeders infamous for keeping animals in poor conditions. Clinton responded with sympathy. “From everything I know about them, they really are terrible places for any animal, and particularly for dogs and cats. We need to do more.”

Animal rights organizations have been trying to do more for half a century. And lately, they’ve found a curious formula for success: Local laws that stop pet stores from selling animals raised at puppy mills.

Puppy mills, which breed about 2 million puppies a year, tend to be clustered in Midwestern states and regulated by state legislatures friendly to agribusiness. About half of those dogs are raised in facilities with U.S. Department of Agriculture licenses, though federal regulations are minimal—they require only, for example, that a cage be six inches bigger than the dog it holds, and that it be cleaned just once a week.

But many of those dogs wind up being sold to consumers in big cities. So activists took the fight to the point of sale.

Albuquerque, New Mexico, led the way in 2006. In the four years that followed, animal adoptions rose 23 percent and euthanasia at city shelters fell by 35 percent. Almost 200 counties, cities, and towns have followed suit, including Boston, Philadelphia, Las Vegas, Los Angeles, Austin, and Salt Lake County, Utah, which encompasses Salt Lake City. Thanks to these new laws, any puppy in the window of those cities’ pet stores is a rescue dog.

In 2013, Phoenix passed its own bipartisan ordinance ensuring that local pet stores sell only dogs and cats from shelters or rescue groups. Tucson, Arizona’s second-largest city, approved a similar ordinance.

This year, the pet-raising industry found a rebuttal: a state-level bill that explicitly withdrew the ability of Arizona’s cities to regulate pet breeding. The law, which Gov. Doug Ducey signed in May, is an example of a pre-emption, a tactic that rural state legislators have used to overrule local control on issues from paid sick leave to gun control.

“Shutting down the good guys will do nothing to stop the bad actors,” Ducey wrote in a letter explaining why he’d approved the bill, noting that he’s a dog owner. “Rather, it will open the doors for more puppy sales through unregulated sources.” He said he favored the state law because it incentivized pet store owners to buy dogs from USDA-approved breeders.

But advocates consider that a paltry guarantee of animal rights. “The USDA is in business to inspect meat in Safeway, not to protect the welfare of dogs in stores,” Tucson Council Member Steve Kozachik told the Arizona Capitol Times. “The governor needs to understand that by signing this bill he’s embracing ‘puppy mill’ standards that the USDA has admitted in its own documents that they are unable to enforce.” (A 2010 review found that the USDA’s Animal Care unit was ineffective in achieving even the agency’s minimal standards.)

At the time, Phoenix was being sued by a couple, Frank and Vicki Mineo, who said the local ordinance would drive the Phoenix location of their store, Puppies ’N’ Love, out of business. State Rep. Brenda Barton, who sponsored an iteration of the pre-emption bill, said Arizona was not about “putting businesses out of business.”

John Goodwin, senior director of the Humane Society’s “Stop Puppy Mills” campaign, says that in reality, the sale of puppies makes up only about 2 percent of pet store revenue. All but one of the top 25 pet store chains in the U.S. and Canada, he said, have stopped selling dogs from commercial breeders.

Several states have also opted to regulate commercial dog breeding. Pennsylvania did so in 2008. The state’s deputy secretary for dog law enforcement (what a job!) described conditions in the state’s breeding facilities to the New York Times the next year. “The dogs never exercise, are subjected to extremes of heat and cold, lack veterinary care and suffer from splayed paws as a result of having to stand on wire mesh rather than a solid floor,” the paper wrote. “At some kennels, cages are stacked, causing dogs in lower cages to be covered in feces and urine from those above.”

There’s momentum at the state level to confront this problem. This year, the New Jersey Senate has approved, with a veto-proof majority, a bill regulating pet dealers in the state. (It now heads to the state assembly.) Louisiana has passed a bill clamping down on puppy mills that includes a provision allowing the state’s cities and parishes to enact stricter local laws as they please.

But the Arizona model, too, has its imitators. Just days after Ducey signed the bill, lawmakers in Ohio—a big state for puppy mills—proposed laws to pre-empt local ordinances that restrict the sale of puppy-mill dogs. Two Ohio cities, Toledo and Grove City, had passed Phoenix-style ordinances, hoping to push buyers toward shelter dogs or small-scale breeders who sell directly to consumers. Those cities may soon find their decisions overruled by the Legislature in Columbus.