WASHINGTON—The Federal Reserve said it will expand its review of Capital One Financial Corp.'s plan to buy ING Groep NV's U.S. online-banking business, ING Direct USA, amid a chorus of complaints and questions.

The Fed set up three meetings to help it collect more information on the proposal. They will be held in Washington, D.C., on Sept. 20; Chicago on Sept. 27; and San Francisco on Oct. 5. In addition, the Fed said it has extended the period for public comment on the proposal through Oct. 12.

The...