Q : What authority do SAVE have to collect my information?

Congress mandated that USCIS provide a system that verifies the immigration status of an individual who is applying for certain types of federally funded benefits in various statutes as provided below:
 
Immigration Reform and Control Act of 1986 (IRCA), P.L. 99-603, dated November 6, 1986:
IRCA required the creation of a system for verifying the immigration status of non-citizen applicants for, and recipients of, certain types of federally funded benefits, and to make the system available to federal, state, and local benefit issuing agencies and institutions that administer such benefits.

Personal Responsibility and Work Opportunity Reconciliation Act of 1996 (PRWORA), P.L. 104-193, 110 Stat. 2168, dated August 22, 1996:
PRWORA required the establishment of regulations and interim guidance for the verification of immigration status of persons applying for “Federal public benefits.”

The Illegal Immigration Reform and Immigrant Responsibility Act of 1996 (IIRIRA), P.L. 104-208, dated September 30, 1996:
The IIRIRA required a means to respond to inquiries by federal, state, and local benefit issuing agencies and institutions seeking to verify or determine the citizenship or immigration status of any individual within the jurisdiction of the Agency for any lawful purpose.