Use this form to show they have adequate means of financial support and are not likely to rely on the US government for financial support. Completing and signing Form I-864 makes you the sponsor.In this guide, we will explain who needs to complete Form I864, when to file it, and how to fill out Form I864 stepbystep. These forms and instructions are available in the General Clerk's Office, Room 108, in the Nassau County. Form I-864 is required for most family-based immigrants and some employment-based immigrants to show that they have adequate means of financial support. For example, if the intending immigrant is also the sponsor's spouse, write. "1" in the "persons you are sponsoring" box but leave the "spouse" box blank. The "Affidavit of Support" is a signed document to accept financial responsibility for a family member who is seeking a green card. The purpose of the Affidavit is to assist consular officers in determining whether a visa applicant will have adequate means of financial support in the US. The information below will help you fill out the form.