Can anyone show me a law that states this? Really don't know how to research the actual case
Your task might be difficult, because the person you are trying to educate already knows what they're doing is wrong.
He or she just believes they're too smart to get caught.
I suggest you simply have the person call, or you can call DMV and ask the question while he or she listens on a speakerphone mode!!!!
Each of the 50 United States and the few odd territories that issue drivers licenses advise at the time of issuance that it is legal to possess ONLY one valid license.
It is known that people circumvent these laws, but do so at great peril.
You are barred from seeking, possessing, or obtaining a license in another state, while under suspension or revocation in any US state.
This what PA says about possessing more than one valid license and revocations/suspensions:
(2) The applicant has held such a license, but the same has been revoked by reason, in whole or in part, of a violation and if such revocation has not terminated, except that after the expiration of one year from the date the license was revoked such person may make application for a new license if permitted by law. The licensing authority may refuse to issue a license to any such applicant if, after investigation, the licensing authority determines that it will not be safe to grant to such person the privilege of driving a motor vehicle on the public highways.
(3) The applicant is the holder of a license to drive issued by another party state and currently in force unless the applicant surrenders such license.
(c) Limitation on number of licenses.--No person shall receive a driver's license unless and until the person surrenders to the department all valid licenses in the person's possession issued by this or any other state. The department shall either return surrendered licenses issued by another state to that state or submit a list of the surrendered licenses to the state, together with information that the person is licensed in this Commonwealth. No person shall be permitted to have more than one valid driver's license issued by this or any other state at any time. A nonresident who holds a nonresident commercial driver's license issued by the Commonwealth under Chapter 16 (relating to commercial drivers) shall be permitted to have a regular driver's license issued by the country of his residence.
http://www.dmv.state.pa.us/pdotforms/vehicle_code/chapter15.pdf
This is how its promulgated in FL:
(b) All surrendered licenses may be returned by the department to the issuing jurisdiction together with information that the licensee is now licensed in a new jurisdiction or may be destroyed by the department, which shall notify the issuing jurisdiction of such destruction. A person may not have more than one valid driver's license at any time.
http://flsenate.gov/Laws/Statutes/2011/322.03