The biggest U.S. banks created more than 10,000 subsidiaries in the past 22 years as they expanded, using legal structures to pay lower taxes and escape tighter regulation, according to a Federal Reserve study.

JPMorgan Chase & Co., the largest U.S. lender, has the most units at 3,391, followed by Goldman Sachs Group Inc., Morgan Stanley and Bank of America Corp. with more than 2,000 each, the study by the Federal Reserve Bank of New York shows. Citigroup Inc., the third-largest lender, has 1,645.

Critics including Thomas Hoenig, a Federal Deposit Insurance Corp. board member, say the biggest firms are too complicated to manage. The 2010 Dodd-Frank Act asked the FDIC and Fed to make sure the largest banks, if they get into trouble, can be wound down without collapsing the rest of the financial system. U.S. Senator Sherrod Brown has proposed legislation to force their breakup.