Most banks program their systems to stop honoring transactions on the specified date, but Wells Fargo allows accounts to remain open for two more months, according to current and former employees. Customers usually learn what happened only after their overdrawn accounts are sent to Wells Fargo’s collections department.

If the customers do not pay the overdraft fees, they are reported to a national database like Early Warning Services, which compiles names of delinquent bank customers. That often means a customer cannot open a new bank account anywhere, and getting removed from the lists can take hours’ worth of phone calls.

One current Wells Fargo employee who spoke on the condition of anonymity said two workers in a debt-collection office complained about the problem through the bank’s anonymous ethics hotline late last year. One, a member of a 40-person office, had collected an estimated $100,000 as a result of the practice, making up 5 percent of the employee’s total collections over an eight-month period.

There are several ways the balance of an ostensibly closed account can fall below zero. They often involve an unexpected payment from the account, such as a gratuity later tacked on to a restaurant bill paid with a debit card. But fraud is another common culprit, according to current and former employees.

Matthew Valles, a former employee who is suing the bank claiming he was wrongfully fired, said he tried to raise an alarm about the overdraft problem in 2017, because it seemed to most frequently affect fraud victims, who often had little or no money to begin with. And a current employee recalled receiving a complaint from a fraud victim who said he was told he owed $4,000 in fees after his checking account was closed.

Fraud victims are particularly vulnerable to the overdraft problem: Those that are tricked into depositing bogus checks, for example, can easily end up having their accounts closed with a negative balance because they unwittingly spend the money before the fraud is discovered.