A federal judge on Monday rejected U.S. Senator Lindsey Graham's challenge to a subpoena to testify before a grand jury in Georgia probing efforts by former President Donald Trump and his supporters to overturn his 2020 election defeat.

Graham, a Republican, had argued his position as a U.S. senator provided him immunity from having to appear before the investigative panel.

"The court finds that the District Attorney has shown extraordinary circumstances and a special need for Senator Graham's testimony on issues relating to alleged attempts to influence or disrupt the lawful administration of Georgia's 2022 elections," U.S. District Judge Leigh Martin May wrote in an order on Monday.

Trump has falsely claimed that rampant voter fraud caused his loss in Georgia, a battleground state where President Joe Biden's victory helped propel him to the White House.

A special grand jury in Fulton County, Georgia, is undertaking a criminal investigation into alleged wrongdoing. It is one of the most serious cases facing Trump, who was recorded in a Jan. 2, 2021, phone call pressuring a top state official to "find" enough votes to overturn his loss to Biden in the state.

Trump has denied any wrongdoing.

The grand jury had also subpoenaed members of Trump's former legal team, including personal lawyer Rudy Giuliani.

Fulton County District Attorney Fani Willis had requested the special jury in January in part due to its subpoena power, which she argued was needed to compel witness testimony.

The Georgia probe is one among several legal troubles faced by the former president, whose Florida home was searched by federal agents last week and whose role in the Jan. 6, 2021 attack on the Capitol is being probed separately by a congressional panel.