Washington — Federal prosecutors have asked the chief judge in Washington, D.C.’s federal court to compel former Vice President Mike Pence to comply with a grand jury subpoena and testify as a witness in special counsel Jack Smith’s investigation into the events surrounding the Jan. 6, 2021 attack on the Capitol, three people familiar with the investigation told CBS News.

The motion to compel Pence’s testimony — filed in secret to Chief Judge Beryl Howell in recent days — came after lawyers for former President Donald Trump asserted executive privilege in response to Pence’s subpoena, the people said. 

That assertion of executive privilege on Pence’s subpoena, the people added, is in line with how Trump’s team has responded to related subpoenas over the past year, with Trump’s attorneys often arguing that private conversations or interactions with a president should remain confidential.

The latest filing also comes after Pence has signaled he would oppose a subpoena from Smith’s office.

Pence and his lawyers have also been preparing to invoke the Constitution’s Speech or Debate clause as a means of protecting him from the investigation. That clause protects members of Congress from being questioned about their legislative actions by other branches of the federal government. 

Pence contends his unique role as both a member of the executive branch and president of the Senate — who presided over Congress’ certification of Electoral College votes on Jan. 6, 2021 — would be covered under the clause.

“On the day of Jan. 6, I was acting as president of the Senate, presiding over a joint session described in the Constitution itself. So, I believe that that Speech and Debate clause of the Constitution actually prohibits the executive branch from compelling me to appear in a court, as the Constitution says, or in any other place,” Pence — who is considering whether he will run for president in 2024 — told reporters in Iowa last week. 

“We’ll stand on that principle and we’ll take that case as far as it needs to go, if it needs be to the Supreme Court of the United States,” he added.

The motion to compel testimony filed by the special counsel’s office is the logical next step in a criminal probe, with prosecutors seeking to force a witness or third party to comply with a grand jury subpoena. Filed less than two weeks after news broke that Pence had received the subpoena, the legal document asks the court to uphold the subpoena’s legal authority and indicates Justice Department prosecutors are moving quickly in their attempt to get Pence before a grand jury. 

People familiar with the probe told CBS News in November that the Justice Department had reached out to Pence in connection to Trump’s alleged efforts to overturn the 2020 election and the events of Jan. 6, 2021. 

Pence’s legal team, Trump’s lawyers and federal prosecutors will now likely work behind closed doors and under seal to convince the federal judge that their interpretation of the law is the right one. 

Two people familiar with the investigation say the chief judge has also made a common move during a grand-jury investigation, issuing a court instruction for secrecy, or “gag order,” in recent days. That means all those involved with the probe in any capacity cannot comment on it. 

The moves by the special counsel come as Howell’s term as Chief Judge presiding over all sealed grand juries in Washington, D.C.’s federal court is set to expire in the coming weeks and a new judge will take over. 

Joshua Stueve, a spokesman for Smith’s office, declined to comment. 

A Pence spokesman declined to comment.

A Trump lawyer declined to comment.

The Justice Department’s subpoena of Pence is separate from the ongoing probe into documents with classified markings from the Trump administration found at his Indiana residence. In that case, Pence’s team and prosecutors have worked in tandem to secure the discovered records and later search his residence and an office in Washington, D.C.