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-134 Affidavit of Support is an important supporting document for your non-US immigrant visa request. You are always the sponsor. If you are using a joint sponsor, then each of you will fill out your own I-134 and each supply your supporting financial documents. U.S. citizens may file Form I-129F, Petition for Alien Fiancé, to request a K-1 visa for a foreign fiancé or a K-3 for a foreign national spouse. File Form I-129F at the USCIS Dallas Lockbox facility. For US Postal Service (USPS): USCIS PO Box 660151 Dallas, TX 75266. Form I-129F ("Petition for Alien Fiancé(e)") is the first step towards a K-1 visa for the fiancé of a US citizen, or a K-3 visa for the spouse of a US citizen. Please ensure that your form is up to date and has not expired.