
Quoting
BOR
Payment, as with any mercantile establishment, is thier business decision. Although currency/coins are acceptable, they can pick and choose.
I have looked this up before for other research and, at least in terms of a business, store, etc., they are not required to accept cash as a method of payment, that is straight form the U.S. Treasury's web page.
Yes, you would think the govt. would be different, but seems not?
To answer the Q of how to make them accept them, either file a direct complaint with that office or head man in DC. Filing suit to attempt to have an Order issued to make them comply is, although a legal possibility, it is basically over the top.