WASHINGTON — The government’s new consumer-watchdog agency is launching a probe into costly overdraft fees charged by big banks.

The Consumer Financial Protection Bureau said today that it will ask banks for information about how overdraft fees affect consumers, how overdraft protection is marketed and what information consumers receive.

The probe could result in new rules or even lawsuits if banks are accused of violating consumer laws.

“Overdraft practices have the capacity to inflict serious economic harm on the people who can least afford it,” CFPB Director Richard Cordray said. “We want to learn how consumers are affected, and how well they are able to anticipate and avoid paying penalty fees.”

Banks impose overdraft fees when people spend more money than they have in their accounts. The fees didn’t exist 15 years ago; by 2009, they were generating tens of billions of dollars for banks.

The fees function like extremely high-cost, short-term loans. The cost of averages $30 to $35 per transaction, the CFPB said.

Banks were barred from automatically enrolling customers in overdraft programs for debit card or ATM transactions in 2010, under a rule issued by the Federal Reserve. The rule did not apply to checks and online bill payments.

Banks have responded by marketing overdraft protection aggressively.

Some banks increased their fee income through a practice known as “reordering.” The banks would collect all the transactions in a given day then apply them in order, from largest to smallest. The effect is to maximize the number of transactions that trigger a fee.