The Justice Department is preparing to bring criminal corruption charges against Democratic New Jersey Sen. Robert Menendez.

Prosecutors allege that the New Jersey senator used his Senate office to push the business interests of donor and friend Salomon Melgen in exchange for gifts.

News of the charges, leaked to CNN, means the shadow of criminal proceedings has fallen on the Senate's leading proponent of Iran sanctions just three days after Israeli Prime Minister Benjamin Netanyahu enraged President Obama and many Democrats by blasting the administration's nuclear negotiations with Tehran.

Attorney General Eric Holder has signed off on prosecutors' request to proceed with the charges, CNN reported. Because of the statute of limitations on some of the allegations, prosecutors are under pressure to officially announce the charges in the coming weeks.

One of the charges focuses on trips Menendez took to the Dominican Republican in 2010 as a guest of Melgen. When word of the public investigation became public in 2013, Menendez paid Melgen $58,000 for the plane trips, citing "oversight" as a failure to properly disclose them. Since then, Menendez, one of the highest ranking Hispanic members of Congress and former chairman of the Senate Foreign Relations Committee, has denied any wrongdoing in his ties to Melgen, a Florida ophthalmologist who has donated generously to both the senator and committees he has been associated with.

Menendez is one of the few Democrats who has been vocal on his disagreement with the Obama administration's foreign policy views on Cuba and Iran.

In January, he called the Obama administration's Iran talking points "straight out of Tehran."

"I have to be honest with you, the more I hear from the administration and its quotes, the more it sounds like talking points that come straight out of Tehran," Menendez said at a Senate hearing. "And it feeds to the Iranian narrative of victimization when they are the ones with original sin — an illicit nuclear weapons program, going back over the course of 20 years, that they are unwilling to come clean on."

Last week, Menendez expressed his concern to Secretary of State John Kerry that news "leaking from the negotiations" with Iran will leave the country with "a vast majority of its nuclear infrastructure" as part of the proposed deal.

On Monday, Mendendez told a crowd at the American Israel Public Affairs Committee conference that he disagrees with "those who say the [Israeli] prime minister's visit to the United States is destructive to U.S.-Israel relations."

He did however call on the Senate to wait until after March 24 to vote on bipartisan legislation that would give Congress power to review an Obama administration deal with Iran on nuclear arms. March 24 is the deadline for producing an outline of a nuclear deal with Iran.

Federal prosecutors are also investigating a slew of other evidence, including Melgen's fight with the Centers for Medicare and Medicaid services, as well as Menendez's role in a Dominican Republican government contract for port screening equipment with ties to a Melgen business interest.

"We believe all of senator's actions have been appropriate and lawful and the facts will ultimately confirm that. Any actions taken by Sen. Menendez ... have been to appropriately address public policy issues and not for any other reason," a Menendez spokesperson said in light of the allegations, according to Jonathan Tamari, the Washington, D.C. correspondent for the Philadelphia Inquirer.

Menendez, the highest ranking Democrat on the Senate Foreign Relations Committee, is in his second term.