Wells Fargo has received subpoenas from three different United States attorneys’ offices in the last week, escalating an investigation into how thousands of bank employees came to secretly issue more than a million sham accounts without customers’ consent.

Federal prosecutors in Manhattan and San Francisco sent the subpoenas seeking information on the misconduct, according to two people briefed on the matter who were not authorized to discuss it. Prosecutors in North Carolina are also investigating, one of the people said.

Wells Fargo, one of the nation’s largest banks, with headquarters in San Francisco, recently settled civil charges with regulators and the city and county of Los Angeles last week. The settlement, in which the bank did not admit or deny wrongdoing, included $185 million in fines and a requirement that the bank hire an independent consultant to review its sales practices.

Wells is famous for its practice of selling new accounts to existing customers, and it is the pressure to meet sales quotas and earn bonuses that is seen as the motive for bank employees who set up credit-card and deposit accounts without customers’ permission. So far, 5,300 employees have been fired for their involvement.