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. This tip sheet will help you complete Form I864, Affidavit of Support Under Section 864A of the INA. Detailed.You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. See tips for completing Form I-864. An Affidavit of Support is US Immigration Form I-864. The joint sponsor must also submit Form I864 and meet the income requirements. Line-by-line guidance for properly filling out USCIS's I-864 Affidavit of Support to sponsor an immigrating family member. Attorney David M. Nguyen discusses how to complete USCIS Form I-864, Affidavit of Support. A look at the legal implications of the Form I-864 Affidavit of Support that US sponsors must fill out for immigrating family members. Some sponsors temporarily reside abroad and intend to move to the US once a family member's immigrant visa is issued.