The Humane Society of the United States has helped pass laws to end the sale of puppies in pet stores in three states and more than 365 U.S. cities, counties and towns. But our work doesn’t end there. We also work to help ensure these laws are neither ignored nor evaded.

Recently we focused on a pet store, Just Puppies in Rockville, Maryland, that was illegally selling puppies. This week, the store's license was voided. And in California, we helped close a loophole in the law that some pet stores were using to sell puppy mill puppies as “rescue” animals.

As our investigations of Petland and other puppy selling stores have documented time and again, such stores are almost always fronts for puppy mills---large commercial breeding enterprises that deny the animals in their care the most basic needs. The young puppies frequently endure terrible, inhumane treatment on their way and once they are in the stores. We’ve documented instances of lack of medical care at the stores as well.

In Maryland, where the law went into effect in January this year following a failed legal challenge by pet stores, we discovered that several stores continued to sell puppies, some online or by appointment only. After pressure from us, including complaints filed with the attorney general’s office, most of them eventually changed to a humane business model. But as a Fox 5 DC report last month revealed, three stores continued to sell puppies in clear defiance of the law. These included Just Puppies, which also has a location in Towson, Charm City Puppies in Columbia, and Maryland Puppies Online in Bel Air.

Related: New Maryland law heralds progress against puppy mills nationwide

Now that the Rockville location of Just Puppies has lost its license, we will stay vigilant until authorities make sure the store is complying, which it has not yet done, and we will continue to pressure Baltimore County officials to enforce the law at the store’s Towson location as well. We urge the Maryland attorney general to ensure that all of the stores now in violation comply with state law and convert to a humane model.

In California, where a law ending pet store sales of puppies went into effect in January last year, some stores, we discovered, were taking advantage of a loophole that allowed pet stores to offer rescued dogs. Instead of offering homeless dogs from real rescues and shelters, however, the stores, hand-in-hand with the puppy mill industry, created fake "rescues." These “rescues” then purchased dogs from the same puppy mills the stores used to buy from before the law went into effect and continued to sell them.

Last month, Gov. Gavin Newsom signed a new law we supported that closed this “rescue” loophole.

None of these successes were accomplished alone: dedicated animal advocates contacted lawmakers, visited pet stores that were in violation to file complaints with authorities, and encouraged the media to stay on top of rogue puppy sellers. The fight against puppy mills requires every animal lover to keep their eyes and ears open and to advocate against buying puppies from pet stores and sourcing instead from responsible breeders, rescues and shelters. If our nation is to push ahead and succeed in the fight against puppy mills, it is crucial that we close the puppy-mill-pet-store pipeline for good.

For people interested in learning how to combat puppy mills effectively and lawfully, we periodically offer the Puppy Mill Action Boot Camp. Our latest boot camp, which will be virtual, will be held tomorrow and it is free for all attendees. You can register here and get the tools you need to join the fight against those who exploit companion animals in the worst ways possible. (If you are unable to attend Boot Camp, you can still register and watch the recorded presentations until December 1.)