The circumstances surrounding the petitioner's conviction were as follows. On December 20, 1965, Leary left New York by automobile, intending to take a vacation trip to the Mexican state of Yucatán. He was accompanied by his daughter and son, both teenagers, and two others. On December 22, 1965, the party drove across the International Bridge between the United States and Mexico at Laredo, Texas. They stopped at the Mexican customs station and, after apparently being denied entry, drove back across the bridge. They halted at the American secondary inspection area, explained the situation to a customs inspector, and stated that they had nothing from Mexico to declare. The inspector asked to search the car, examined its interior, and saw what appeared to be marijuana seeds on the floor. Small amounts of marijuana were also found on the car floor and in the glove compartment. A personal search of Leary's daughter revealed a silver snuff box containing semi-refined marijuana and three partially smoked marijuana cigarettes. Though Leary was arrested for violating the Marijuana Tax Act, it was also illegal in the state of Texas to possess marijuana. Hence, compliance under federal law would have provided self-incriminating evidence.
a. If read according to its terms, the Marijuana Tax Act compelled petitioner to expose himself to a "real and appreciable" risk of self-incrimination;
b. [The statute] required him, in the course of obtaining an order form, to identify himself not only as a transferee of marijuana but as a transferee who had not registered and paid the occupational tax;
c. Compliance with the transfer tax provisions would have required petitioner unmistakably to identify himself as a member of [a]..."selective" and "suspect" group, we can only decide that when read according to their terms these provisions created a "real and appreciable" hazard of incrimination.