Actually, the number the casino asks for is a TIN (Taxpayer Identification Number). You supply this on IRS form W9, and yes I have filled these out when getting a W2g from a new casino. It is up to you to be sure the number is correct; you don't have to show the casino any other document with your TIN or SSN on it. Of course, the W9 is sent to the Feds and if it doesn't match the name and other ID info you supplied, you and the casino will hear about it!

Even though the Social Security program when initiated assured all the citizens their number would never be used for any other purpose than Social Security, they have reniged on this and your SSN is now your TIN, unless you fit one of the exceptions, like foreign citizenship. When Congress decides to require all babies received an implant with identification information readable electronically, the need for some of these forms will go away. It's just a matter of time .