Catch--22 re the employer who pays with gold/ silver coins: He can get in trouble for violation of the minimum-wage law!

Years ago a Customs officer told me that gold was a "Monetary Instrument" under the reporting law. I don't know if there's any distinction between gold ingots vs. bullion coins with a marked face value. OTOH, Krugerrands are legal tender in South Africa for the daily market price of gold bullion, so are reportable to US Customs at bullion value as money.
In fact, it was forbidden to import Krugerrands into the USA in the late 1980s when South Africa was embargoed under sanctions to punish the apartheid regime.