Moody's decision to downgrade the credit rating of 28 Spanish banks means more problems for Europe as it tries to dig out of the growing debt crisis.
Spain's government recently asked for help to clean up its ailing banking sector. But the rating negatively impacts other nations' measurement of Spain's ability to repay debts.
Spanish banks are also said to be vulnerable to losses from the country's busted real estate bubble.
Spain's economy is the fourth largest of the 17 countries that use the euro. The unemployment rate there is nearly 25 percent.
President Barack Obama recently urged Europe to move faster to fight the debt crisis because it's affecting the global economy.
Germany Finance Minister Wolfgang Schauble responded, saying the U.S. is even worse shape.
"Mr. Obama should first of all take care of reducing the American deficit, which is higher than in the eurozone," he said in an interview Sunday night.
The eurozone's debt is about 80 percent of the economy compared to about 100 percent in the U.S.