The STOP Improper Licensing Act requires the Federal Motor Carrier Safety Administration to audit how states issue non-domiciled commercial driver's licenses, with a focus on identifying licenses wrongly given to people who no longer have legal presence in the United States or who were never verified for lawful presence. The Administrator must complete the initial audit within three years, then publish findings and give states 30 days to respond, with a final report due to Congress within 90 days. States found to have compliance problems must implement corrective measures within 60 days or submit a corrective action plan, and the Administrator will conduct follow-up audits based on error rates—annually for states with error rates above 25 percent for three years, or after two years for those with rates between 10 and 25 percent. States that fail to respond or come into compliance face withholding of all federal motor carrier safety funding, and the Administrator must notify Congress each time a state is found in substantial noncompliance or returns to compliance.