New Jersey Administrative Code 13:20-32.7 -> (d) A motor vehicle, other than a police vehicle or a motor vehicle for which a medical exemption certificate has been issued by the Division in accordance with N.J.S.A. 39:3-75.1 et seq., shall not be certified which has tinted spray or plastic material added to previously approved glazing in the front windshield or windows, vents, wings, deflectors, or side shields to the immediate right or left of the driver, because such condition changes the vision and light transmission properties of the glazing in areas where driver visibility shall not be obscured or obstructed; provided, however, tinted spray or plastic material may be applied to previously approved glazing in the front windshield if such spray or material extends no lower than six inches from the top of the front windshield or such spray or material does not extend below the AS-1 marking on the front windshield.
When a New Jersey registered vehicle has a valid inspection sticker displayed and there's after-market tint; the following statutes can be issued: 39:3-47 (Altering after inspection) and 39:3-77 (Unapproved Equipment).
When a New Jersey registered vehicle does not have a valid inspection sticker and there's after-market tint; the following statutes can be issued: 39:8-1 (Failure to Inspect) and 39:3-77 (Unapproved Equipment).
39:3-77 Unapproved Equipment or Devices
1. No person shall sell, offer or use any unapproved device or equipment for use on a motor vehicle.
FN1: Administrative Code permits window tint behind the driver; however, unless that after-market tint was previously "approved by the commissioner" (which it never is) - it would be a violation.
Also, click this, in reference to law concerning installers of Tint:
http://www.njleg.state.nj.us/2002/Bills/AL03/21_.PDF