(Reuters) - About two-thirds of U.S. banks are either already taking measures to limit the growth in their balance sheets or would take steps to cap them if they continue growing, a Federal Reserve survey of bank finance officers showed on Thursday. The concerns about the size of their balance sheets reflected in the Senior Financial Officer Survey came as 40% of respondent banks reported faster-than-expected growth in end-of-day reserve balances. The largest factor driving that growth was deposits, which broadly are growing faster than bank officials had estimated. Should banks broadly begin limiting their balance sheets, it could have implications for the availability of bank credit as the U.S. economy pulls out of the recession triggered by the COVID-19 pandemic. “Among the two-thirds of respondents who reported their bank is limiting, or would limit under certain growth assumptions, the size of its balance sheet, almost half rated net interest margin pressure and return on assets as important or very important factors in that decision,” the survey said. Likely measures they may take include allowing outstanding wholesale funding liabilities to mature without replacement and reducing deposit rates on non-operational deposits, according to the survey, which included banks that account for roughly 75% of the reserves in the U.S. banking system. Reporting By Dan Burns; Editing by Chizu Nomiyama Our Standards: The Thomson Reuters Trust Principles.