A group of students last year did their final project on the sentencing rules regarding crack cocaine versus powder cocaine. Essentially the rule said that, to get the same prison terms, powder cocaine offenders (who are typically White and sometimes affluent) needed to have 100 times more cocaine in their possession than crack offenders (who are typically Black). Here is a news story from the L.A. Times about changes to that 100 to 1 rule.
Crack cocaine sentences: U.S. Sentencing Commission reduces prison terms.