Does anyone know if there is a regulation/law requiring U.S. banks to cash U.S. government checks for non-depositors?

There is no such federal law or regulation. Some states (Massachusetts is one) have laws requiring that banks cash certain types of government checks for customers and non-customers. In Massachusetts, the law extends to social security, SSI, and other government (state, federal, and local) retirement payments of up to $2,500.

Thanks, Ken.

I think you mean John.

That's OK, Skittles. I'm flattered to be confused with Ken.