(NEXSTAR) — Former Vice President Mike Pence is expected to resist a subpoena for testimony as part of a Justice Department special counsel’s investigation into former President Donald Trump’s efforts to overturn the 2020 election, a source familiar with Pence’s plans confirmed to The Hill.

Pence is preparing to fight a subpoena from Jack Smith, the special counsel assigned by Attorney General Merrick Garland to oversee investigations into Trump, including one focused on the events of Jan. 6, 2021, and Trump’s efforts to remain in power.

Pence and his team say that serving as the former president of the Senate essentially makes him a member of the legislative branch and he would therefore be shielded from the subpoena under the “speech and debate” clause of the Constitution.

The former vice president’s resistance is likely to result in a legal battle that could end up at the Supreme Court and determine the extent of the powers and independence of the vice presidency.

Politico first reported Pence’s plans to fight the subpoena.

It was reported last week that Smith’s office had moved to subpoena Pence in one of its most aggressive moves to date as its inquiries into Trump accelerate. Smith’s office is also handling an investigation into Trump’s handling of classified documents.

But Pence’s testimony could be critical in the probe into Trump’s bid to overturn the results of the 2020 election, when he lost to President Joe Biden.

Pence, as he detailed in his memoir, was part of numerous conversations where the president and his legal advisers pushed baseless claims about widespread fraud or floated novel and untested legal theories that could be used to keep Trump in the White House.

Pence ultimately refused Trump’s repeated requests to reject the Electoral College results on Jan. 6, 2021, and certified the results of the election hours after rioters had been cleared from the Capitol that day. Pence at the time said there was no constitutional basis for him to reject the election results.

The former vice president has since spoken about his decision that day, but he has also signaled that he would be hostile to attempts from Congress to get his testimony about the events before and during Jan. 6.

While former Pence officials from the White House testified to the House panel investigating the Jan. 6 riots, the former vice president said Congress had “no right” to his testimony.

“We have a separation of powers under the Constitution of the United States,” Pence told CBS News in November. “And I believe it would establish a terrible precedent for the Congress to summon a vice president of the United States to speak about deliberations that took place at the White House.”

Pence is weighing a possible 2024 presidential campaign, with a decision expected in the next few months. The former vice president, who would have to run against Trump to win the nomination, is scheduled to travel to Iowa and Minnesota this week.