The guidelines set by the U.S. Sentencing Commission, which was established by Congress, have been advisory, not mandatory, since the high court's U.S. vs. Booker in 1995.

In the Monday case, Derrick Kimbrough pleaded guilty to possession with intent to distribute more than 50 grams of crack cocaine in Norfolk, Va., as well as several other charges. Under the guidelines, Kimbrough faced 15 years to life in prison.

The guidelines are much harsher for crack cocaine offenses as opposed to powdered cocaine. They suggest the same five-year term whether someone is convicted of distributing 5 grams of crack or of distributing 500 grams of powder.

A federal judge sentenced Kimbrough to 15 years only, citing the "disproportionate and unjust effect that crack cocaine guidelines have in sentencing" raised by the commission's own reports.

A federal appeals court threw out the sentence, saying the crack-powder disparity was not enough to result in the lower sentence.

But the Supreme Court majority ruled that the judge used the proper authority to downsize the sentence, saying the crack-powder disparity was enough to justify that result.