The Federal government has (and has exercised) the power to expand the definition of legal tender. The states do not.
(And that could actually happen. Say the state decides that they don't want to do X, but state or federal law says they have to. Well, fine, but there's a fee for X. The state just requires that you have to pay it in gold or silver.)
https://en.wikipedia.org/wiki/1861_in_the_United_States
The Federal government has (and has exercised) the power to expand the definition of legal tender. The states do not.