You need a CDL to drive a commercial motor vehicle (CMV), which is defined as:
A single vehicle with a gross vehicle weight rating (GVWR) of 26,001 pounds or moreA trailer with a GVWR of more than 10,000 pounds if the gross combination weight rating is 26,001 pounds or moreA vehicle designed to transport 16 or more occupants, including the driver, or a vehicle defined as a busAny vehicle that requires hazardous materials placardsYou can obtain a Class A, Class B, or Class C commercial license, depending on the type of vehicle you will be driving. If you drive a CMV without a commercial license, you could go to jail or incur a court fine of $5,000.
when am I exempt from needing a CDL?
Not all large vehicles require a commercial license. Generally, RVs driven for personal or family recreation, military vehicles driven by the military, farm vehicles driven on farms by farmers, and emergency vehicles driven by emergency personnel are exempt (see section 1 of the New York State Commercial Driver's Manual for specifics).