Federal prosecutors are in the early stages of an investigation into sales practices at Wells Fargo & Co. that led to the bank being hit last week with a $185 million fine, according to people familiar with the matter.

The investigation is being conducted by the U.S. attorney’s offices for the Southern District of New York and the Northern District of California, these people said. Prosecutors have yet to decide if any case, should they decide to pursue one, would be along civil or criminal lines, the people said.

Prosecutors have issued a subpoena to the bank for documents and materials, the people added.

A spokeswoman for Wells Fargo declined to comment. A spokesman for the Manhattan U.S. attorney declined to comment. A spokesman for the U.S. attorney for the Northern District of California didn’t respond to requests for comment.

Wells Fargo last week was fined by the Office of the Comptroller of the Currency, Consumer Financial Protection Bureau and Los Angeles City Attorney and entered into an enforcement action. The regulators alleged that Wells Fargo engaged in “widespread illegal” activity and said that employees had opened as many as two million accounts without customers’ knowledge. The bank neither admitted nor denied wrongdoing as part of the settlement.