When you use Form G-639, Freedom of Information/Privacy Act (FOIA) Request, to make a request for information, USCIS has an obligation to ensure the subject of the request is willing to share that information with you. Confirming one’s identity helps ensure the privacy of that person. (Even if you are requesting your own records, USCIS needs to confirm your identity.)
Therefore, USCIS requires that the subject of the request consents to sharing information. On Form G-639, two options are provided:
A Notarized Affidavit is a type of verified statement made by the subject and witnessed by a notary public. It is a sworn statement of fact that has legal consequences if ever found to be untrue.
A Sworn Declaration Under Penalty of Perjury is a similar promise. It is a sworn statement of fact. By signing this statement, you are swearing its truth and acknowledge that you have potentially perjured yourself if the statement is untrue.