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. An Affidavit of Support is US Immigration Form I-864.Form I-129F: The U.S. citizen sponsor must file Form I-129F, Petition for Alien Fiancé(e), with the United States Citizenship and Immigration Services (USCIS). There are several types of Affidavit of Support forms (I-864, I-864EZ, I-864W, and I-864A). In addition to a complete K-1 visa application form (Form I-129F), you will need to supply the following to U.S. Citizenship and Immigration Services (USCIS):. 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. Form I-864, also known as an affidavit of support, is commonly required during green card application for many categories.