Former Vice President Mike Pence has been issued a subpoena by the special counsel overseeing criminal investigations of ex-President Donald Trump, one of which is focused on Trump’s efforts to overturn the results of the 2020 election, NBC News confirmed Thursday evening.

Pence, who served under Trump, was pressured by him to refuse to accept the certifications of the Electoral College slates of several states that gave President Joe Biden his margin of victory in the 2020 race.

Pence did not agree with Trump’s request when he presided over a joint session of Congress that confirmed Biden’s victory.

That joint session on Jan. 6, 2021, was interrupted for hours by a mob of Trump supporters who stormed the U.S. Capitol, sending Pence and members of Congress fleeing to hide from the invaders. Trump refused for hours requests that he publicly call on his supporters to leave the Capitol.

ABC News first reported that special counsel Jack Smith had subpoenaed Pence. ABC also reported that the subpoena was issued after months of negotiations between federal prosecutors and Pence’s legal team.

It was not clear whether Smith is seeking Pence’s testimony, documents, or both.

Spokesmen for both Pence and Smith declined to comment on the subpoena.

Smith previously issued a subpoena seeking documents from Georgia Secretary of State Brad Raffensperfger, whom Trump had pressured in early 2021 to “find” him enough votes in that state to overcome his ballot deficit to Biden there.

Smith is also investigating Trump for removing White House documents, many of which were classified, and shipping them to his Mar-a-Lago club in Palm Beach, Florida, where he has lived since leaving office.

Smith was appointed special counsel by Attorney General Merrick Garland after Trump declared his candidacy for the 2024 Republican presidential nomination.