The Supreme Court ruled last week that legal residents can only be deported under the Immigration and Nationality Act for acts that are felonies under the Controlled Substance Act, and not merely felonies under state law. In Lopez v. Gonzales the court ruled "Conduct made a felony under state law but a misdemeanor under the CSA is not a "felony punishable under the Controlled Substances Act" for INA purposes."
For more information about the underlying case see the Cornell preview. In this case, the government still has the discretion to initiate removal proceedings, but Lopez' prior conviction cannot be designated as a felony. See also our page on Immigration.