The other is that, with respect to certain federal crimes, a prior conviction for an aggravated felony provides a sentencing enhancement.

When he was released, the INS sought to deport him because, it claimed, he had been convicted of a controlled substances violation and an "aggravated felony."

A "drug trafficking crime," in turn, refers to "any felony punishable under the Controlled Substances Act [the CSA] (21 U.S.C.

To answer this question, the Court had to parse the phrase "any felony punishable under the Controlled Substances Act."

Since it did not, the Court reasoned, the class of crimes that constitute aggravated felonies must be defined in federal law.

In the Court's opinion, Government's gloss on the statutory phrase was not consistent with ordinary English usage.

The Government pointed out that the term "aggravated felony" applies to any offense "whether in violation of Federal or State law."

This qualification, it argued, showed that Congress intended for state law to determine whether conduct qualified as an aggravated felony.

Justice Thomas accepted the Government's interpretation of the phrase "felony punishable under the Controlled Substances Act."