Policy Memorandum: Exceptions for Permitting the Filing of Form I-601, Application for Waiver of Grounds of Inadmissibility, and Any Associated Form I-212, Application for Permission to Reapply for Admission into the United States After Deportation or Removal, at International USCIS [open pdf - 262KB]
"This policy memorandum (PM) provides guidance and procedures regarding the circumstances when it is permissible for international USCIS [United States Citizenship and Immigration Services] managers to allow the filing of a Form I-601 and any associated Form I-212."
Policy Memorandum: PM-602-0062
U.S. Citizenship and Immigration Services: http://www.uscis.gov/