[bjtitus]

I would have sworn I've read the opposite but found this history [1] outlining usage of SSNs:

> Private sector use of the SSN is neither specifically authorized nor restricted. People are asked for an SSN at banks, video rental outlets, hospitals, etc., and may refuse to give it. However, the provider may, in turn, decline to furnish the product or service, leaving some to conclude they have no real choice.

> Throughout the history of the Social Security program, the SSN, originally intended to be used only to record Social Security earnings, has been adopted for other purposes, both governmental and private. The broad-based coverage of the Social Security program makes the SSN widely available and a convenient common data element for all record-keeping systems and data exchanges.

[1] https://www.ssa.gov/history/reports/ssnreportc2.html