Thousands of small business owners were reportedly impacted by the improper sales practices at Wells Fargo, according to Sen. David Vitter, a Louisiana Republican.

Last week, Vitter, who also heads the U.S. Senate's small business committee, sent a letter addressed to Wells Fargo CEO John Stumpf demanding a full list of customers affected. "Fraudulent activity of your employees was not limited to Wells Fargo's consumer banking operations," he wrote in the letter, which was reviewed by Reuters on Tuesday, explaining that the revelations came during congressional staffer discussions with the bank.

Several business owners who discovered unapproved accounts in their name, extra fees, or lower credit scores, have since moved to other banks. About 10,000 small businesses were affected by the account fraud, according to sources cited by Reuters.

Wells Fargo is also facing lawsuits from former employees, shareholders, and customers. The bank has said it is changing its sales practices, and recently removed the sales goal incentives that led to fraud. But customers and industry watchdogs are now on alert.

"This was outrageous conduct. It was a violation of trust and an abuse of trust. It should not have happened," Richard Cordray, director of the Consumer Financial Protection Bureau, told CNBC last month. "I guarantee you that we will be seeing that it does not happen again at any bank."


This story was updated to clarify Senator Vitter's comments.