When Brian P. Brooks was a financial regulator during the first Trump administration, he would hear complaints about “debanking” and force himself not to roll his eyes.

The expression was being used by representatives of some rather polarizing businesses, such as private prisons and fracking operators, who complained to Mr. Brooks, the acting comptroller of the currency, that their bank accounts were being closed without warning. His reaction boiled down to the free-market equivalent of tough luck. He didn’t see it as his job to compel banks to do business with anyone in particular.

Five years later, Mr. Brooks, who now runs a brokerage firm and advises cryptocurrency companies, says he is convinced there is a problem. He is among a growing number of people in the finance world who have urged Trump administration officials over the past half-year — in meetings in Washington and at the Mar-a-Lago club in Florida — to crack down on the practice.

“The electric company can’t deny you service because it doesn’t like your looks, and neither can a bank,” Mr. Brooks said in an interview.

In recent months, the cry of “debanking” has rung out from conservative and religious groups and the Trump Organization to accuse lenders of politically motivated discrimination. It is coming from cryptocurrency companies that say regulations bar them from opening ordinary bank accounts, and from liberal lawmakers speaking up for individuals and businesses whose A.T.M. cards are shut off without warning.