@ThelmaLou, what specific circumstances are we talking about in terms of providing proof?
I mean, for example, in recent political news the SAVE act provision which crashed and burned, had distinct requirements for proof:
Eligible documents include a REAL ID-compliant identification indicating U.S. citizenship; a valid U.S. passport, military ID and service record; a government-issued photo ID showing U.S. birthplace; or a government-issued photo ID that does not indicate birthplace or citizenship and a valid secondary document…
Employers often require similar verification, but different reasons for proving citizenship may use different criterea.