Using such messaging services for official government business could violate the Presidential Records Act, which requires that nearly all official White House correspondence be preserved.
Some participants at the ethics sessions in the Old Executive Office Building said Passantino suggested that there had been inappropriate use of smartphone apps such as WhatsApp.
"He did focus on WhatsApp — said that people were using it, and it wasn't appropriate," said one staffer who attended a recent briefing and requested anonymity to describe the discussion. "He said, 'All those apps are a big problem.' "
Passantino declined to comment, but White House officials disputed that description of his remarks. Although he noted that executive branch employees should not use such platforms for official business, they said, he did not assert that officials had been relying on them in the past.
"Regular ethics briefings are a critically important part of a much larger initiative designed to ensure that all White House personnel hold themselves to the highest possible ethical standards," White House spokeswoman Lindsay Walters said. "It's disheartening to see the false accusations of anonymous sources outweigh the truth of what was actually said in the briefing."
Passantino instructed anyone who received work-related communications on unofficial platforms to forward them to their White House email so official administration business could be preserved, according to people in attendance. A White House official said Passantino used the example of a staffer who receives a work-related question on a private Gmail account, saying that employee should reply and copy his or her government email to ensure that communications are steered to official accounts.
In addition, he reminded aides to preserve White House records and not conduct political activities that could violate the Hatch Act, these people said.
The reminder came as the White House contends with a lawsuit filed in June by the watchdog group Citizens for Responsibility and Ethics in Washington (CREW), which alleges that the administration is failing to comply with records laws because of past reports that aides have used messaging apps to communicate.
The Trump administration has argued that the case should be dismissed because courts do not have authority to review the executive branch's compliance with the law.
CREW lawyer Anne Weismann said the White House ethics sessions reinforce her group's case.
"They know that these apps are being used; they know the requirements of the Presidential Records Act are not being met," she said. "I guess I will claim some victory. . . . If they are in fact now training people and monitoring compliance, that's a good thing."
The recent focus on appropriate communication channels came as part of mandatory ethics training sessions the White House Counsel's Office has been leading for all executive staff since early January.
Trump's son-in-law and senior adviser, Jared Kushner, attended a session last month, according to people familiar with his participation. Last year, an attorney for Kushner confirmed that he used a private email account to discuss official White House business during his first nine months in government service. Those messages were forwarded to his official email account for preservation, the attorney said.
Other administration officials seen in the recent ethics briefings were White House lawyer Ty Cobb, national security adviser H.R. McMaster, homeland security adviser Tom Bossert and several members of the White House press office.
The sessions coincide with a ban on use of personal cellphones inside the White House, a policy that administration officials said was directed by White House Chief of Staff John F. Kelly to improve security and was fully implemented last month. Staffers said that when they arrive for work each morning, they are instructed to deposit their personal phones in lockers installed at White House entrances. A senior White House official said all messaging apps have been deactivated on government phones.
In February 2017, The Washington Post reported, staffers were using Confide to discuss internal White House operations out of fear of being accused of leaking information to the media. The Confide app deletes messages as soon as they are read.
The following month, then-House Oversight Committee Chairman Jason Chaffetz (R.-Utah) and ranking Democrat Elijah E. Cummings of Maryland sent a letter to the White House seeking assurances that the Trump administration was complying with the presidential records law.
In response, White House legislative affairs chief Marc Short wrote that the administration was "committed" to retaining work records.