The First Circuit has determined that an immigration judge may inquire into the bona fides of a marriage that is the basis of an application for adjustment of status, even after U.S. Citizenship and Immigration Services has approved an immediate relative petition based on the marriage. The court noted that an immigration judge has a duty to determine if an applicant for adjustment of status is admissible, which includes ruling out that the applicant has committed marriage fraud.
The full text of Chan v. Lynch can be found here: http://media.ca1.uscourts.gov/pdf.opinions/15-2112P-01A.pdf