NEW YORK ( TheStreet) -- Overdraft penalties are a big source of earnings for many banks, and an important regulatory change that kicks in shortly may put those profits in jeopardy. Beginning July 1 for new accounts and Aug. 15 for accounts opened before July 1, banks will need to get customers to agree to pay overdraft fees before they can be assessed. The regulatory change was announced by the Federal Reserve in November. Analysts at Sandler O'Neill wrote in a recent report on the issue that banks are "optimistic" customers will agree to the fees rather than run out of cash at the ATM. But banks still need to get customers to respond to mailings asking them to opt in. Sandler ran some data on 117 banks and thrifts to see which get the biggest boost to core operating revenues from service charges, a big chunk of which comes from overdraft fees. Although none of the four largest retail banks appeared in the top five, it is worth noting that Citigroup ( C) and Bank of America ( BAC), two banks that often get lumped together by investors, are very different in terms of how heavily they depend on service charges. Citigroup gets just 1% of its core operating revenues from service charges, which translates to it being less reliant on service charges than every bank on the list that Sandler looked at except Oriental Financial Group ( OFG), which also comes in at 1%. Bank of America, on the other hand, gets 12% of its core operating revenues from service charges, tying it for seventh place with a host of other banks. Here are the five banks most reliant on the revenues they get from service charges, according to Sandler's report. The revenue and earnings figures cited are based on trailing averages for the past four quarters.