This form must be filed with a U.S. Citizen Petition for a Preference Relative to Become a Lawful Permanent Resident. The form must also be filed with a U.S. Citizen Petition for an Immediate Relative to Become a Lawful Permanent Resident
For both preference and immediate relative petitions, the applicant must file form I-130. They may also need to file Form I-485. Your immigration lawyer can help you file all the correct forms and fill out each form correctly.
According to the USCIS, the affidavit of support, I-864, is essentially a contract where the individual signer agrees to use their financial resources to help support the immigrant named in the petition who is seeking US immigration status. The signer of the I-864 becomes the immigrant’s sponsor once that immigrant becomes a lawful permanent resident.
The law that governs the affidavit of support is the Immigration and Nationality Act (INA).
The Affidavit of support form can be viewed at https://www.uscis.gov/i-864