A U.S. federal agency has opened a formal investigation into former special counsel Jack Smith, who oversaw two criminal probes into U.S. President Donald Trump following his first term in the White House.

The Office of Special Counsel (OSC) confirmed to Reuters that it was investigating whether Smith violated the Hatch Act, a law prohibiting federal employees from using their position for political activity. The decision follows a request for a probe by U.S. Sen. Tom Cotton, an Arkansas Republican.

The OSC is an independent agency that probes the conduct of federal employees, but it does not have the authority to bring criminal charges. It is different from the type of Special Counsel's office previously overseen by Smith, who was appointed by the Department of Justice to pursue criminal cases.

The office's investigation, which was first reported by the New York Post, is the latest in a series of actions taken by Trump and his allies against their perceived political enemies.

Smith, who resigned from his post in January following Trump's election victory, could not immediately be reached for comment.

Earlier this week Cotton accused Smith of aggressively pursuing his cases against Trump with the aim of hurting his presidential campaign, calling Smith "a political actor masquerading as a public official," in a series of posts on social media platform X.

"That's why I've asked this unprecedented interference in the 2024 election be immediately investigated by OSC," Cotton wrote.

A former war crimes prosecutor, Smith brought two criminal cases against Trump — one accusing him of illegally retaining classified material and another related to Trump's attempts to overturn his 2020 election loss, an effort that sparked the Jan. 6, 2021, assault on the U.S. Capitol.

Neither case went to trial, having been delayed and buffeted by a series of legal challenges, including a ruling by the U.S. Supreme Court's conservative majority that granted former presidents broad immunity from criminal prosecution.

Smith dropped both cases after Trump won last November's election, citing a long-standing Justice Department policy against prosecuting a sitting president, but he issued a report in January saying the evidence he gathered would have been enough to convict Trump at trial.

Trump denied wrongdoing and assailed the prosecutions as politically motivated attempts to damage his campaign.