As someone who lives in the US I was initially outraged that a SSN was being required by an airline, especially since this number is tied into every aspect of ones credit and therefore not to be handed out especially to a airline. But I eschewed venting opting instead for a Google search which seems to suggest that this may be a Brazilian thing. It appears a Brazilian CPF (Social Security Number) may be required for domestic--and Argentina is a neighbor--flights. I did not require this on a US bought ticket (twice) between Sao Paulo and Rio. But I am curious.