"In the Department of Transportation and Related Agencies Appropriation Act of 1992,100 Congress required the withholding of ten percent of certain federal highway funds unless a state either: 1) enacts and enforces a law revoking or suspending for at least six months the driver's license of an individual who is convicted of any drug offense; or 2) the governor submits written certification to the Secretary of the Department of Transportation that he or she opposes the revocation/suspension, and that the state legislature has adopted a resolution expressing its opposition to this law.l01 This law defines "drug offense" as any criminal offense involving the possession, distribution, manufacture, cultivation, sale, transfer, or the attempt or conspiracy to possess, distribute, manufacture, cultivate, sell, or transfer any substance (the possession of which is prohibited by the Controlled Substances Act) or the operation of a motor vehicle under the influence of such a substance.102
"Thus, unless states formally express their opposition to the federal law, they must suspend or revoke for at least six months the driver's license of anyone convicted of a drug offense.103 If they do express their opposition, they are free to limit suspension or revocation only to offenses involving driving or other more limited categories of offenses. Twenty-three states automatically suspend or revoke drivers' licenses for conviction of some or all drug offenses, in addition to driving-related offenses;104 the other twenty-seven states do not."
Mukamal, Debbie A. and Samuels, Paul N., "Statutory Limitations on Civil Rights of People with Criminal Records." Fordham Urban Law Journal (New York, NY: Fordham University, 2002) Volume 30, Issue 5, p. 1515.