Carriers need an IFTA license if they operate a qualified motor vehicle across two or more member jurisdictions (all of US except Alaska, Hawaii, and DC and most Canadian provinces). A qualified motor vehicle is any vehicle with a GVWR/GCWR over 26,000 lbs or a vehicle of any weight with three or more axles.
Carriers with an IFTA license are required to file a quarterly return with their base state.
Late payment fees will be assessed if you file/pay after the deadlines.
Most jurisdictions now allow you to file your returns using an internet based program either directly through your base state or via an authorized third party. For those states in which online filing is not available a paper return must be mailed.