If the underwear was made in China or India or another foreign country, the importation of it violated customs laws. DHS, specifically their ICE (”C” is for customs, “E” for enforcement) which used to be part of the old CBP, does indeed have jurisdiction.
Doesn’t mean that they don’t have better things to do, of course.
I’ve always walked thru Sears and seen tables filled with panties that had the Garfield cartoon character printed on them, and wondered who the adult women were who actually bought them.
They might have more important things to do,
but this is far easier than confronting Islamic terrorism.