Not many people would knowingly pay more than $35 for a cup of coffee. But far too many people are getting saddled  with no warning  with outsized bills for minor purchases, under a euphemistically labeled “overdraft protection program” that most major banks have adopted over the last 10 years.

Before that, most banks would simply have rejected debit transactions, without a fee, when the card holder’s account was empty. Now, they approve the purchase and tack on a hefty penalty for each transaction.

Moebs Services, a research company that has conducted studies for the government as well as some banks, reported recently that banks will earn more than $38 billion this year from overdraft and bounced-check fees. Moebs also estimates that 90 percent of that amount will be paid by the poorest 10 percent of the customer base.

Federal regulators who stood idly by while this system evolved are considering new overdraft rules that could provide more transparency. If they do not move quickly and aggressively to protect consumers, Congress should step in.