WASHINGTON (AP) — The National Archives has asked former U.S. presidents and vice presidents to re-check their personal records for any classified documents following the news that President Joe Biden and former Vice President Mike Pence had such documents in their possession, two people familiar with the matter said Thursday.

The Archives sent a letter Thursday to representatives of former presidents and vice presidents extending back to Ronald Reagan to ensure compliance with the Presidential Records Act. The act states that any records created or received by the president are the property of the U.S. government and will be managed by the archives at the end of the administration, according to the two people, who spoke on condition of anonymity because they were not authorized to speak about investigations.

The Archives sent the letter to representatives of former Presidents Trump, Barack Obama, George W. Bush, Bill Clinton, George H.W. Bush and Ronald Reagan, and former Vice Presidents Pence, Biden, Dick Cheney, Al Gore and Dan Quayle.

The letter was first reported by CNN.

Spokespeople for former presidents Barack Obama, George W. Bush and Bill Clinton and former vice presidents Mike Pence, Dick Cheney, Al Gore and Dan Quayle did not immediately respond to requests for comment.

Biden’s lawyers came across classified documents from his time as vice president in a locked cabinet as they were packing up an office he no longer uses in November. Since then, subsequent searches by the FBI and Biden’s lawyers have turned up more documents. Former Vice President Mike Pence, too, this week, discovered documents and turned them in after saying previously he did not believe he had any.

The White House did not immediately respond to a request for comment but the searches by Biden’s attorneys and the FBI appear to fulfill the Archives’ request.

Handling of classified documents has been a problem off and on for decades, from presidents to Cabinet members and staff across multiple administrations stretching as far back as Jimmy Carter. But the issue has taken on greater significance since former President Donald Trump willfully retained classified material at his Florida estate, prompting the unprecedented FBI seizure of thousands of pages of records last year.

Attorney General Merrick Garland appointed a special counsel to investigate Trump’s handling of the documents, and also Biden’s.

Speaking Thursday at an unrelated news conference, FBI Director Christopher Wray said that though he could not discuss any specific ongoing investigation, “We have had for quite a number of years any number of mishandling investigations. That is unfortunately a regular part of our counterintelligence division’s and counterintelligence program’s work.”

He said there was a need for people to be conscious of laws and rules governing the handling of classified information. “Those rules,” he said, “are there for a reason.”

WASHINGTON — In a show of solidarity and bipartisanship, former presidents Barack Obama, George W. Bush and Bill Clinton and their wives joined President Joe Biden and Vice President Kamala Harris at Arlington National Ceremony Wednesday afternoon.

Biden and Harris laid a wreath at the Tomb of the Unknown Soldier. The wreath was made of green leaves with red and white blooms. Each took a moment of silent prayer standing in front of the tomb before stepping back.

The former presidents announced last week they would attend the ceremony. Former President Donald Trump did not attend, he left Washington, D.C. earlier Wednesday morning and did not attend any inaugural events.

More than 400,000 service members, veterans and their families are buried in Arlington National Cemetery.