“You want these limits so there is some kind of market discipline on these banks,” said Mr. Cannon. “If I were on the F.D.I.C. board, I would be concerned about this.”

The F.D.I.C. has not taken any position on the cash management companies, but a spokesman said that it was important to ensure strict record-keeping to preserve a full accounting of where the deposits ended up.

Tom Nelson, the chief investment officer at Reich & Tang, said that by spreading money among banks, his firm and others like it increased the stability of the banking system and that the practice “reduces the risk of runs on banks.”

The F.D.I.C. guarantee was one of a number of factors that encouraged depositors to shift money into noninterest bearing accounts after the crisis. Since 2011, when the account guarantee program was extended as part of the Dodd-Frank financial regulation law, the amount of money in such accounts rose by 70 percent, or $678 billion, according to Alex Roever, a JPMorgan Chase analyst.

The vast majority of the holdings in these accounts are above the $250,000 limit and are held in the nation’s largest banks. That money is expected to stay put no matter what, in part because corporations and municipalities widely believe that the government will step in if those large banks encounter trouble, effectively considering them too big to fail.

In recent months, as the deadline loomed, community banks lobbied fiercely for the program to be extended, arguing that it helped level an uneven playing field that favored large banks. The smaller banks said that without the unlimited guarantee, the nation’s largest banks would win an even greater concentration of total customer deposits. Congressional leaders at first appeared ready to continue the guarantee, but this December decided against it, saying that it threatened to allow more bank bailouts.

Before the latest financial crisis wiped out hundreds of banks and left Wall Street teetering on the brink of collapse, many depositors were comfortable keeping large sums in accounts even if there was no government guarantee. But with the memory of bank failures still fresh, customers are more aware of the inherent risks involved.