Four years ago, Wal-Mart abandoned its plans to obtain a long-sought federal bank charter amid opposition from the banking industry and lawmakers, who feared the huge retailer would drive small bankers out of business and potentially conflate its banking and retail operations. Ever since, Wal-Mart has been quietly building up à la carte financial services, becoming a force among the unbanked and “unhappily banked,” as one Wal-Mart executive put it.

Even before the recent outcry against banks, the services had become popular with cash-poor customers, many of whom never had a bank account and found the services more affordable than traditional check-cashing operations. Now newcomers to the ranks of the banking disaffected are helping to swell the numbers, Wal-Mart officials said.

The run from banks is happening elsewhere, too. In the last four weeks, as anger over debit card fees festered, more than 650,000 customers signed up for credit unions, according to the Credit Union National Association. The association was still tallying how many additional consumers had signed up on Bank Transfer Day, an initiative on Saturday that took shape after Kristen Christian, a banking customer upset by fees, set up a Facebook page.

“We have a tremendous opportunity ahead of us, and it’s largely due to what you’re seeing around us happen in the industry,” said Daniel Eckert, the head of Wal-Mart Financial Services. “We’re not a bank, but we can serve a lot of types of functions you would see someone go into a bank for.”

Wal-Mart says it has no intention of reviving its plans to become a full-blown bank that could make loans and accept federally insured deposits. But the retailer has obtained bank charters in both Mexico and Canada, leading some bankers to suggest the company is laying similar groundwork in this country.