UPDATE: Sen. Ayotte released the following statement regarding her signing the letter:

“A nuclear-armed Iran would pose a serious threat to the United States, Israel, and the world, and I am deeply concerned that the agreement the Obama administration is pursuing would allow Iran to continue its acts of regional terrorism and simply delay – and not dismantle – its nuclear weapons program. Congress led the effort to impose the toughest possible sanctions, which brought Iran to the negotiating table. With so much at stake, I believe the Senate should have an opportunity to review any agreement reached between the U.S. and Iran and vote to approve or disapprove that agreement.”

New Hampshire U.S. Sen. Kelly Ayotte was among the 47 Republican Senators who signed a letter to Iran about ongoing nuclear talks.

NPR reports: "Coming two weeks before the deadline to reach general terms with Iran, the signatories wrote that they had been observing the negotiations over potentially relaxing the economic sanctions - and told Iran's leaders they were concerned 'that you may not fully understand our constitutional system.'"

The letter cautions Iran that any deal struck that is not approved by Congress is "nothing more than an executive agreement between President Obama and Ayatollah Khamenei."

"The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms of the agreement at any time," the letter reads.

Freshman Arkansas Sen. Tom Cotton wrote the letter, and Ayotte was among the Senators who co-signed it.

The White House expressed strong opposition to the letter.

President Obama said, "I think it's somewhat ironic to see some members of Congress wanting to make common sense with the hard-liners in Iran" who are also against making a deal over Iran's nuclear program.

Iranian Foreign Minister Mohammad Javad Zarif called the letter a "propaganda ploy."

"In our view, this letter has no legal value," he said.