Sen. Marco Rubio Marco Antonio RubioOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats step up hardball tactics as Supreme Court fight heats up Press: Notorious RBG vs Notorious GOP MORE (R-Fla.) is asking Attorney General William Barr Bill BarrHarris faces pivotal moment with Supreme Court battle Hillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE to investigate if former Secretary of State John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE broke federal law over his talks with Iranian officials.

Rubio sent a letter to Barr doubling down on his request for the Justice Department to investigate Kerry, a request he also made last year to then-Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE.

"The Department of Justice should therefore make a determination on whether or not former Secretary of State John F. Kerry’s recent actions related to the Joint Comprehensive Plan of Action with Iran potentially violate the Logan Act or the Foreign Agents Registration Act," Rubio wrote in the letter to Barr.

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He added that "the American people deserve to know that U.S. laws are enforced regardless of any individual’s past position."

Rubio's letter comes after President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE and Kerry locked horns last week.

Trump told reporters late last week that Kerry should be prosecuted under the Logan Act for speaking with Iranian officials and criticizing Trump's policies in Iran.

"What I’d like to see with Iran, I’d like to see them call me," Trump said. "John Kerry speaks to them a lot, and John Kerry tells them not to call. That’s a violation of the Logan Act, and frankly he should be prosecuted on that."

The Logan Act bans private citizens from negotiating with foreign governments without permission from the U.S. Violating the obscure law is a felony, but only two people have ever been charged with doing so and nobody has ever been convicted.

A spokesperson for Kerry told CNN that "everything President Trump said today is simply wrong, end of story."

"He's wrong about the facts, wrong about the law, and sadly he's been wrong about how to use diplomacy to keep America safe," the spokesperson added.

Kerry helped negotiate the nuclear deal between the U.S. and several world powers with Iran during the Obama administration, a deal Trump pulled out of last year.

The former secretary of State said last year that he had met with Iran's foreign minister "three or four" times since leaving office to discuss the nuclear pact, among other issues.