What is the difference between an order compelling a third party to produce information as part of a criminal investigation and a subpoena compelling that third party produce information once a criminal proceeding has commenced?

difference between orders compelling a third party to produce information as part of an investigation, and orders compelling a third party to produce information once a criminal proceeding has commenced. Although subpoenas issued in connection with pending litigation or the grand jury process are not normally considered final (United States v. Ryan, 402 U.S. 530, 532533, 91 S.Ct. 1580, 29 L.Ed.2d 85 [1971] ), and even nonparties to those proceedings who wish to obtain immediate appellate review of a subpoena must first defy the order, be held in contempt, and then appeal the contempt order (id. at 532, 91 S.Ct. 1580 ), that rule is inapplicable to district court orders enforcing a subpoena issued by a government agency in connection with an investigation.