Iran has announced that it no longer accepts US dollars for oil.
Most of the world's oil transactions are conducted in dollars, which benefits the US by providing a ready-made market for dollar denominated securities and allowing the US to run large current accounts deficits.
However, that started to change as countries began abandoning the so-called petrodollar system. Iraq began trading oil for euros in 2000 (and was invaded not long after), and Venezuela began trading oil for anything not long after.
Two months ago, partly as a rebuke against American threats and interference, Iran opened the Iranian Oil Bourse (IOB), an oil trading market priced in currencies other than the dollar.
Iran has been threatening to abandon the dollar for some time, and the IOB was launched to begin diversifying away from dollars.
Now Iran has phased out dollars completely and is also unloading its dollar denominated foreign exchange reserves.