Only if you are selling used panties. They might be considered a biohazard. Understand it's not your used panties specifically that would be a biohazard, just used panties in general.
Check out this link from the US Department of Health and Safety:
http://dohs.ors.od.nih.gov/shipping_...tm#generalinfo
They should be specifically labeled, marked, and documented to avoid confiscation and possibly fines.