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.You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. See tips for completing Form I-864. This video will help you to fill out I-864 For Joint Sponsor. A joint sponsor - also called a co-sponsor - has the same liability under an Affidavit of Support as a primary sponsor. 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 Form I864, Affidavit of Support is required in virtually all familybased immigration cases. Financial sponsors for green card applicants use Form I-864, Affidavit of Support, to remove the public charge grounds for inadmissibility. USCIS evaluates a sponsor's income using Form I-864, Affidavit of Support.