Interoffice Memorandum: Guidance on Evaluating a Request for the Rescheduling of an Interview and Handling the Failure of an Applicant, a Petitioner, a Sponsor, a Beneficiary, or Other Individual to Appear for a Scheduled Interview (AFM Update AD06-01) [open pdf - 88KB]
"This memorandum provides United States Citizenship and Immigration Services (USCIS) field offices with instructions on evaluating a request for the rescheduling of an interview and handling the failure of an individual to appear for a scheduled interview. This memorandum supersedes any previous guidance addressing these aforementioned issues. If an individual requests an interview to be rescheduled or fails to appear for a scheduled interview, USCIS field offices are directed to implement immediately the procedures outlined in the 'Field Guidance' section of this memorandum and either reschedule the interview or deny the related application or petition accordingly."
U.S. Citizenship and Immigration Services: http://www.uscis.gov/