*sigh* So much misinformation being disseminated.

Its not illegal to sell snails in the US. Its not illegal to transport most snails across state lines (with the possible exception of apple snails). It is, however, now being regulated and one needs to get a permit to do so. Some LFS/LPSes don't want to bother with the permits, so they are telling their customers that its now illegal for them to do so. I've researched it on the government websites and this is the information I got. And yes, its because they are invasive and idiots have been releasing them in the wild where they, particularly apple snails, have become a serious nuisance issue.