From Great Smoky Mountain NP website (similar restrictions found on many public lands here in the southeast)
"Firewood Regulations: Only heat-treated firewood that is bundled and certified by the United States Department of Agriculture (USDA) or a state department of agriculture may be brought into the park."
Note: There is a difference between 'heat treated' and 'kiln dried'.
I don't have a problem with this given the effect the Emerald Ashe Borer and Woolly Adelgid have had on our Ashe and Hemlock forests. These restrictions along with the increased cost of legitimate firewood led us to purchase a propane campfire although I still prefer real wood when possible.