Copper prices are down sharply on worries that Europe's financial bailout plan could be undermined by Greek voters.

Copper for December delivery fell 3.6 percent Tuesday to settle at $3.5025 a pound. That puts copper down nearly 6 percent this week.

Prices fell after Greek Prime Minister George Papandreou announced that he would put an unpopular European financial rescue package for his country to a popular vote. If the vote fails, it might lead the country into a messy default and threaten Europe's plan for staving off a financial crisis.

Copper prices rose last week on hopes that the European plan would shore up banks and foster economic growth. That would increase demand for raw materials like copper.

Gold fell 1 percent to $1,711.80 an ounce.