Five banks in the Denver area, all of them branches of Chase, received threatening letters on Monday, at least one of which contained a white powder, the Denver Post reported.
The newspaper's website quoted a spokesman for the Denver Fire Department as saying the white powder did not appear to be dangerous, reported Reuters.
Police confirmed that several banks had received letters but had no further details.
The Post said hazardous materials crews were sent to at least one bank, which was shut down because of the threat.