Wells Fargo was fined $185 million US for the scandal involving employees who earned bonuses by creating bank accounts for customers without their knowledge. (David Paul Morris/Bloomberg)

The CEO of Wells Fargo apologized to U.S. senators today for a multi-year scam in which more than 5,000 bank employees were signing customers up for bank accounts without their knowledge, in order to earn commission-based bonuses.

John Stumpf showed contrition in testimony to the Senate Banking Committee on Capitol Hill, saying he is "deeply sorry" that the bank failed to meet its responsibility to customers and didn't act sooner to stem "this unacceptable activity." He promised that the bank will contact every affected customer, even though it is still in the process of sifting through all its accounts to determine which ones might be affected.

More than 1.5 million bogus bank accounts were set up, along with more than 500,000 credit cards over a period of at least five years.

Alabama Republican Senator Richard Shelby, chair of the banking committee. said Wells Fargo had a corporate culture "that drove company 'team members' to fraudulently open millions of accounts using their customers' funds and personal information without their permission."

New senior executives have been fired or otherwise left the company in relation to the scandal, CEO John Stumpf said Tuesday. (Pete Marovich/Bloomberg)

"If there were ever a textbook case where consumers needed protecting, this was it," Shelby said.

Many senators said the bank's actions amount to fraud, something Stumpf denies, instead characterizing the actions as "wrongful" and "unacceptable."

Some of the harshest questions came from Massachusetts Democratic Senator Elizabeth Warren, who dismissed Stumpf's claim he was taking accountability for the scandal.

She told Stumpf, "You should resign, you should give back the money you made while this scam was going on, and you should be criminally investigated," and described his inaction after the story came forward as "gutless leadership."

Sen. Warren blasts <a href="https://twitter.com/search?q=%24WFC&src=ctag">$WFC</a> CEO: "You should resign...and you should be criminally investigated..." <a href="https://t.co/uSB5UB6H6s">pic.twitter.com/uSB5UB6H6s</a> —@CNBCnow

Stumpf said during the hearing that the company's board "has the tools to hold senior leadership accountable," including himself and Carrie Tolstedt, former head of the retail banking business.

2 million fake bank accounts made up

Tolstedt announced in July her retirement from the bank this year. She's expected to leave with as much as $125 million US in salary, stock options and other compensation.

Wells Fargo has long been known for its aggressive sales goals, but the details and the $185-million fine that regulators imposed last week have singed the consumer banking giant's reputation as a well-run, tightly managed company removed from the reckless conduct on Wall Street that stoked the financial crisis.

In some cases, the customers' own money was moved in and out of the bogus accounts without their knowledge. Debit cards were issued and activated, and PINs were created, without telling customers. In some cases, bank employees even created fake email addresses to sign up customers for online banking services, the regulators said.

The bank boasts about its "cross-sale" ratio being abnormally high. The average U.S. bank user has between five and six different accounts. Wells Fargo's ratio is more than eight.

Executive bonuses

"This was not the work of a few rogue employees over the course of a few weeks," several Democrats on the banking committee wrote in a letter to Stumpf last week. "Wells Fargo had a long-standing, systemic problem created by stringent sales quotas and incentives imposed by senior management."

Wells Fargo employees signed their customers up for two million bank and credit accounts without their knowledge, the bank recently admitted. (CX Matiash/Associated Press)

Under the settlement, Wells Fargo neither admitted nor denied the allegations. It later said it plans to eliminate the sales targets by Jan. 1.

The panel also plans to question regulators from the Consumer Financial Protection Bureau, the Treasury Department's Office of the Controller of the Currency and the Los Angeles City Attorney's Office. Senators are examining their role in the debacle and why the sales practices went on for years before the regulators cracked down.