Here are some links to the laws:Federal MandateIPPC Standards FAQISPM 15
Also, keep in mind that many pallets are used for international shipping. While most industrialized countries have an NPPO, not all do. That means the country may not comply with the standards of other countries.
For the most part, if you stick by these guidelines and don't make a food cutting board from a pallet, you should be safe using them for projects.
As with any project involving cutting wood, you should always use a mask to keep from breathing in particles and pollutants.