By Executive Order
The Roosevelt Gold “Confiscation” of 1933
From the article:
Using the rationale that hoarding of gold was hurting the depression economy, President Franklin D. Roosevelt signed Executive Order 6102 prohibiting private ownership of gold. Signed in April, it required citizens to redeem their gold coinage at banks by May 1, where they would receive paper currency in exchange. A $20 double-eagle gold coin would fetch a $20 Federal Reserve Note. (This was because gold was trading at $20.67 per Troy ounce, and a double-eagle contained .9675 Troy ounces of gold.)
The penalty for not redeeming gold coins was severe – 10 years in prison and/or a $10,000 fine.