Most states, including Virginia, have licensing requirements for contractors. Virginia's requirements apply regardless of trade and regardless of whether the contractor is a prime contractor or one of the prime's lower tier subcontractors.
Unlike some other states, Virginia has a 3-level "class" system for contractors, based - in general - on contract value: $10,000 or less = Class C; $10,000 or more up to $120,000 = Class B; and more than $120,000 = Class A (similar to an "unlimited" license in some other jurisdictions). Not only are there civil penalties for being unlicensed, but it is also a crime. There are certain exceptions, but rarely would they apply to a commercial project.
Besides being a crime, from a practical standpoint, non-licensure can also affect entitlement to payment. Non-licensure was previously judicially held as a total bar to payment in Virginia (and still is in North Carolina), but a key statute was revised to allow non-licensure as a defense to payment (but not the rest of the code requirements) if, even if not licensed, the contractor: 1) substantially performed with the contract terms; 2) in good faith; and 3) without actual knowledge of the licensure requirements.
It is always important to determine whether your contractor is licensed. There are sound practical reason for licensure, and while a license alone does not insure good workmanship, it is at least an indicator that the contractor has had requisite training and is not "fly by night."
Conversely, if you are a contractor, it is important be be licensed. Not only is there the practical issue of entitlement to payment for your work, but non-licensure also establishes the basis for civil penalty, and criminal prosecution.
More information about Virginia's licensure requirements is available at the Virginia Board for Contractor website: http://www.dpor.virginia.gov/dporweb/con_main.cfm.
License holders can be looked up on line at the Virginia Department of Professional and Occupational Regulation: