WASHINGTON – The Justice Department cited Apple in February 2018 over an account belonging to Donald F. McGahn II, then President Donald J. Trump’s attorney in the White House, and banned the company from telling him about it, so two people into the Thing briefed.

Apple told Mr. McGahn of the subpoena last month, said one of the people who spoke on condition of anonymity to discuss the matter. Mr McGahn’s wife also received a similar notice from Apple, the person said.

It is not clear what FBI agents were investigating, whether Mr. McGahn was their particular focus or whether he was swept into a larger web for communicating with someone under surveillance. As the top attorney for the 2016 Trump campaign and then as a White House attorney, Mr. McGahn was in contact with numerous people who may have been caught during the Russia investigation or a later leak investigation.

Still, the disclosure that agents had collected data from an incumbent White House attorney that they kept secret for years is exceptional.

And it comes amid a political backlash following revelations that the Trump administration secretly seized the personal information of reporters and Democrats in Congress from phone and tech companies while investigating leaks.

Democratic leaders on Capitol Hill on Sunday increased pressure on the Justice Department and former officials to provide a fuller account of the events. They called on Justice Department head, John C. Demers, and former Assistant Attorney General Rod J. Rosenstein, along with former Attorney General Jeff Sessions and William P. Barr, to testify before Congress.

A Justice Department spokesman declined to comment, as did a lawyer for Mr. McGahn. An Apple representative did not respond to a request for comment.

Apple informed Mr. McGahn that it complied with the subpoena in a timely manner, but declined to tell him what it had provided the government with, according to one person who was briefed on the matter. According to Justice Department guidelines, toggle orders for subpoenas can be extended for up to a year at a time, suggesting that prosecutors went to court multiple times to prevent Apple from notifying the McGahns sooner.

During investigations, agents sometimes compile a large list of phone numbers and email addresses that have been in contact with an individual and attempt to identify each of those individuals by submitting subpoenas to communications companies for account information such as names, computer addresses, and associated credit card numbers credit with you.

Apple informed the McGahns that it received the subpoena on February 23, 2018, according to one person who was brought up on the matter.

Federal law generally requires prosecutors to seek permission from a federal judge to force a company like Apple to delay notifying people of their personal information being subpoenaed, said Paul M. Rosen, a former federal prosecutor and partner at Crowell and Moring.

“There is a lot here that we do not know, including the facts and circumstances surrounding the request for delay and what was presented to the judge,” said Mr Rosen. He added that prosecutors usually have to prove that either notifying the person would “jeopardize someone’s safety, destroy evidence or intimidate witnesses, or seriously jeopardize an investigation.”

The subpoena was issued by a grand jury in the Eastern District of Virginia, said the other person familiar with the matter.

It is not clear why the prosecution received the subpoena. But several notable developments took place around that time.

The federal court in the Eastern District of Virginia was the center of a portion of the Russia investigation, led by Special Counsel Robert S. Mueller III, that focused on Paul Manafort, a former chairman of the 2016 Trump presidential campaign.

Since Mr McGahn was the top Trump campaign attorney in 2016, it was possible that he had been in contact with someone earlier, whose account the Mueller team was closely investigating in early 2018.

Notably, the day before the subpoena, Mr. Manafort was hit with new fraud allegations in the Eastern District of Virginia. Later developments showed that Mr. Mueller’s investigators scrutinized some of his communications reports closely in the days that followed.

On the flip side, the Manafort case was largely handled in the District of Columbia, where it faced separate charges. Still, during this time, the Mueller team also worked with the Virginia federal prosecutor’s office on an unregistered case by a foreign agent related to Turkey and a business partner of Michael T. Flynn, former National Security Advisor to Mr. Trump, who also served him during the 2016 advised campaign.

At the same time, Mr. McGahn was also involved in another matter related to the Russia investigation, which included a leak.

In late January 2018, the New York Times reported, based on confidential sources, that Mr Trump had previously directed Mr McGahn to have Mr Mueller removed from the Department of Justice in June, but Mr McGahn had refused to do so and threatened to resign . The Washington Post confirmed this report in a follow-up article shortly afterwards.

The Mueller report – and Mr McGahn in a private testimony before the House Judiciary Committee earlier this month – described Mr Trump’s anger at Mr McGahn after the Times article and how he had tried to persuade Mr McGahn to make a statement that she did wrongly denied. Mr. Trump told his aides that Mr. McGahn was a “liar” and a “leaker,” according to former Trump administration officials. In his testimony, Mr. McGahn said that he was a source for The Post’s successor to clarify a nuance – to whom he had communicated his intentions to resign – but he was not a source for the original Times article.

However, there are reasons to doubt that Mr. McGahn was the target of a Justice Department leak investigation resulting from this episode. For example, information about Mr Trump’s order to fire Mr Mueller does not appear to be a classified secrecy that it could be a crime to disclose.

Another incident that occurred around the same time was an investigation by the Ministry of Justice into unauthorized disclosure of information about the Russia investigation. As part of this investigation, prosecutors sent Apple a subpoena on February 6, 2018 with data on Congress officials, their families, and at least two members of Congress. Apple only recently informed the target persons because it was prohibited from disclosing the subpoena at the time.

Among those whose data was seized were two Democrats on the House Intelligence Committee: Representatives Eric Swalwell and Adam B. Schiff, both from California. Mr. Schiff, a sharp political opponent of Mr. Trump, is now the chairman of the panel. The Times first reported on the subpoena last week.

Many questions about the events leading up to the subpoenas go unanswered, including how highly authorized they were in the Trump Justice Department and whether investigators expected or hoped they would bring in data on the politically prominent lawmakers. The subpoena was looking for data on 109 email addresses and telephone numbers.

In this case, the leak investigation appeared to have focused primarily on Michael Bahar, then a member of the House Intelligence Committee. People close to Mr. Sessions and Mr. Rosenstein, the two senior Justice Department officials at the time, said neither of them knew that prosecutors had requested data on the accounts from lawmakers for this investigation.

It remains unclear whether agents were pursuing a theory that Mr. Bahar had leaked on his own, or whether they suspected him of speaking to reporters with the approval of lawmakers. Either way, it seems they couldn’t prove their suspicions that he was the source of unauthorized disclosures; The case has been closed and no charges have been brought.

Spokeswoman Nancy Pelosi called on Mr. Barr, Mr. Sessions and Mr. Rosenstein on Sunday to testify before Congress about the subpoenas. She said what the Justice Department did under Mr. Trump “went beyond Richard Nixon,” but declined to say whether a congressional committee would compel her testimony.

“Let’s hope they want to honor the rule of law,” she said. “The Justice Department was a villain under President Trump.”

New York Senator Chuck Schumer, the majority leader, called on anyone who might be involved in the subpoenas, including Mr. Demers, to testify before Congress. “The sins of the Trump administration continue to pile up,” he said at a press conference in New York.

“This was nothing less than a gross abuse of power, an attack on the separation of powers,” said Schumer, warning that the legislature would summon them if the men did not testify.

He also called on Senate Republicans to join the Democrats and vote for subpoenas from Congress to compel testimony.

On CBS, Republican Senator Susan Collins of Maine called the allegations “serious,” but said only that she supported an investigation into the matter by the independent Justice Department inspector announced on Friday.

Katie Benner, Adam Goldman and Luke Broadwater contributed to the coverage.