By Sadie Gurman and Siobhan Hughes

WASHINGTON -- The Justice Department's internal watchdog and Senate Democrats vowed to investigate the Trump administration's secret seizure of communication records of people associated with the House Intelligence Committee.

Inspector General Michael Horowitz said Friday his office would conduct a probe, as Senate Majority Leader Chuck Schumer (D., N.Y.) and Senate Judiciary Committee Chairman Dick Durbin (D., Ill.) called for former attorneys general Jeff Sessions and William Barr to testify before Congress about the revelations.

In May, tech giant Apple Inc. notified individuals associated with the committee that the Justice Department had issued grand-jury subpoenas for their information in February 2018, according to a House committee official. The committee immediately contacted the Justice Department for clarification and additional information, the official said, adding that the department informed the committee last month that the matter had been closed.

At the time of the subpoenas, then-President Donald Trump and officials in his administration, including Mr. Sessions, were trying to locate the source of leaks about contacts between Russia and figures in Mr. Trump's 2016 election campaign.

Mr. Barr, Mr. Trump's second attorney general, inherited about a half-dozen leak investigations when he took office in 2019. He directed a federal prosecutor from New Jersey to work on the cases, which had languished under his predecessor, and then brief top officials, a person familiar with the matter said.

On Friday, Mr. Barr sought to distance himself from the developments, saying he hadn't been aware of leak cases in which there were subpoenas related to lawmakers' communications. "I didn't recall that case," Mr. Barr told The Wall Street Journal. "Whatever steps were taken, were taken before I arrived."

Other former officials said the Justice Department had been investigating whether a House Intelligence Committee staffer leaked classified information, but that probe was closed last year without charges. The officials added that it wasn't clear whether that matter was related to the subpoenas issued to Apple.

The Justice Department occasionally investigates and charges members of Congress in corruption investigations, but legal experts on national security issues said there is no precedent for investigating members for leaking national security information. Most rules governing the handling of classified information are established under a president's executive authority, and aren't laws. Little precedent exists for whether members of Congress -- as officers of a coequal branch of government -- must comply.

"To my knowledge, no member of Congress has ever been prosecuted for unauthorized disclosures of classified information," said Bradley Moss, a national-security lawyer in Washington.

"Any indictment would be fraught with constitutional implications," Mr. Moss said. "There'd be fights over separation of powers. There'd be fights over abuse of authority."

Members of Congress also have immunity from prosecution based on actions taken in their official capacity in Congress, under the U.S. Constitution. In 1971, then-Sen. Mike Gravel entered the highly classified Pentagon Papers into the congressional record -- an action that sparked a federal grand jury investigation, but no charges were brought against the senator.

Reports of the subpoenas follow earlier revelations that the Justice Department under Mr. Barr subpoenaed the records of reporters at several news organizations including the Washington Post, the New York Times and CNN.

The Justice Department said it would no longer seek records of reporters' contacts when investigating government leaks of sensitive information.

Mr. Horowitz, the department's inspector general, said his office would also examine those cases. His announcement came after Attorney General Merrick Garland and his deputy, Lisa Monaco, requested the watchdog examine the department's handling of leak cases.

Mr. Horowitz said he would examine whether the subpoenas or investigations were "based on improper considerations."

"The reported conduct of the Department under Attorney General Barr is shocking, and clearly fits within an appalling trend that represents the opposite of how authority should be used," said White House spokesman Andrew Bates.

Sens. Schumer and Durbin said in a statement that other officials who were involved must also testify before the Senate Judiciary Committee under oath. "We expect that our Republican colleagues will join us in getting to the bottom of this serious matter," they said.

At least one Senate Republican on the committee would need to join Democrats in voting to issue a subpoena because Democrats don't have the power to unilaterally issue subpoenas. The chamber is evenly divided at 50-50. "I am somewhat doubtful that we would get a Republican, but it's a possibility -- I wouldn't rule it out," said Sen. Richard Blumenthal (D., Conn.), a member of the Senate Judiciary Committee.

"The Justice Department must provide information and answers to the Judiciary Committee, which will vigorously investigate this abuse of power," the statement said.

The Judiciary Committee includes Sen. Ben Sasse (R., Neb.), who earlier this year voted to convict Mr. Trump of inciting an insurrection on Jan. 6 and voted to create a commission to investigate that day's attack on the Capitol. The commission was blocked due to opposition by other Senate Republicans.

Obtaining the contents of communications generally requires a search warrant.

Apple has made privacy protections for users a cornerstone of its business. The Justice Department sought to force Apple to create software that would allow investigators to unlock the iPhone of the perpetrator in a 2015 San Bernardino, Calif., terrorist attack. The company refused, and ultimately the two sides avoided a courtroom showdown when the Federal Bureau of Investigation used an outside party to gain access to the device.

Even as it refused to unlock phones, Apple regularly complies with court orders for information in the U.S. and abroad. In the first six months of 2020, the latest year in which data was available, Apple complied with thousands of requests for account and device access, according to figures the company discloses on its website.

Apple said it wasn't provided any context for the Justice Department investigation when it was first served a subpoena in 2018, only that the government sought customer or subscriber account information from 73 phone numbers and 36 email addresses. The information was limited to metadata and didn't provide any content such as emails or pictures, the company said.

Apple would normally have informed the affected customers immediately, but the Feb. 6, 2018, federal grand jury subpoena, signed by an assistant U.S. attorney, included a nondisclosure order prohibiting the company from disclosing the existence of the subpoena or informing the individuals, Apple said. The yearlong nondisclosure order was extended three times, it said. When the order wasn't extended for a fourth time, Apple informed the customers on May 5, 2021.

House Speaker Nancy Pelosi and House Intelligence Committee Chairman Adam Schiff have called for an investigation into the Justice Department's pursuit of the communications data, first reported by the New York Times. It reported that the records of at least a dozen people connected to the panel in 2017 and early 2018, including those of Mr. Schiff, were seized in the probe.

The House Intelligence Committee has continued to seek additional information from the Justice Department, the House committee official said, adding that "DOJ has not been forthcoming in a timely manner, including on questions such as whether the investigation was properly predicated and whether it only targeted Democrats."

Byron Tau, Tim Higgins, Aruna Viswanatha and Ken Thomas contributed to this article.

Write to Sadie Gurman at sadie.gurman@wsj.com and Siobhan Hughes at siobhan.hughes@wsj.com

(END) Dow Jones Newswires

06-11-21 2129ET