The Justice Department’s independent inspector general opened an investigation on Friday into the decision by federal prosecutors to secretly seize the data of House Democrats and reporters as investigators hunted down who was leaking classified information early in the Trump administration.

At the same time, top Senate Democrats demanded that the former attorneys general Jeff Sessions and William P. Barr testify publicly before Congress about the leak investigations, including about subpoenas issued to tech companies in 2017 and 2018 for the records of at least a dozen people tied to the House Intelligence Committee. The senators vowed to “vigorously investigate” and called on Republicans to join them.

Apple, which complied with a subpoena for information related to more than 100 email addresses and phone numbers in February 2018, said on Friday that it did not realize that the records belonged to Representative Adam B. Schiff of California, the top Democrat on the Intelligence Committee, and his associates. Microsoft said it was also subpoenaed by a grand jury as early as November 2017 for data related to an email account for an aide to the panel.