Yup, what ladycat said. They ship live chicks, to cross state lines they have to be NPIP, no if's ands or buts.
When you look at their websites/info they have a symbol/stamp like square icon that says NPIP. They each have their own NPIP number and you can verify it with the states NPIP contact.
ETA: It is the backyard flock owner with who certification is optional, but again to ship you need to be certified. Also each state may have it's additionals, like in TN if I had more than 3000 chickens I'd have to get a business license and certify because of that.