U.S. Vice President Joe Biden lashed out at Republican lawmakers for their “highly misleading” letter Monday to Iran’s leaders cautioning against a nuclear deal with the United States.

U.S. Vice President Joe Biden lashed out at Republican lawmakers for their “highly misleading” letter Monday to Iran’s leaders cautioning against a nuclear deal with the United States.

“The letter sent on March 9th by 47 Republican Senators to the Islamic Republic of Iran, expressly designed to undercut a sitting president in the midst of sensitive international negotiations, is beneath the dignity of an institution I revere,” Biden said in a statement.

On Monday, the Republican senators warned Iran’s leaders that any nuclear deal with President Barack Obama could last only as long as he remains in office, an unusual partisan intervention in foreign policy that could undermine delicate international talks with Tehran.

The open letter was signed by all but seven of the Republicans in the Senate and none of Obama’s fellow Democrats, who called it a “stunt.” Iranian Foreign Minister Javad Zarif dismissed it as a “propaganda ploy” from pressure groups he called afraid of diplomatic agreement.

In the letter, the senators said Congress plays a role in ratifying international agreements. Noting Obama will leave office in January 2017, they said any deal not approved by Congress would be merely “an executive agreement” that could be revoked by Congress.

‘Without precedent’

A Western diplomat said the action was “without precedent.” “It’s 100 percent an American issue, but obviously it could become a real problem,” the diplomat said.

Iran’s Zarif blasted the Republicans. “I wish to enlighten the authors that if the next administration revokes any agreement ‘with the stroke of a pen’ … it will have simply committed a blatant violation of international law,” he said in a statement.

The letter seemed to harden partisan lines in the Senate, where Republicans will need Democrats’ support to pass legislation now in the works to tighten sanctions on Iran or require congressional approval of a deal.

“Republicans are undermining our commander in chief while empowering the ayatollahs,” said Democratic Minority Leader Harry Reid.

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