The Collaborative International Dictionary of English v.0.48:

criminalize \criminalize\ v. t.
   to declare (an act) to be illegal.

   Syn: outlaw, illegalize, ban.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

criminalize
    v 1: treat as a criminal
    2: declare illegal; outlaw; "Marijuana is criminalized in the
       U.S." [syn: outlaw, criminalize, criminalise,
       illegalize, illegalise] [ant: decriminalise,
       decriminalize, legalise, legalize, legitimate,
       legitimatise, legitimatize, legitimise, legitimize]