In a highly unusual move, 47 Republican senators sent an open letter to Iran, warning the country that any deal struck with President Barack Obama won't be set in stone. Now that letter has offended some Democrats and the Iranian government from Tehran.

According to a report from Fox News, Vice President Joe Biden denounced the letter on Monday night, arguing that it "offends me as a matter of principle" and the action was "beneath the dignity of an institution I revere." The letter was originally sent by Sen. Tom Cotton, R-Ark., and 46 of his fellow Republican colleagues.

"In 36 years in the United States Senate, I cannot recall another instance in which senators wrote directly to advise another country - much less a longtime foreign adversary - that the president does not have the constitutional authority to reach a meaningful understanding with them," Biden said in his statement. "The decision to undercut our president and circumvent our constitutional system offends me as a matter of principle."

Fox News reported that Biden, who made a lengthy statement on the matter, was part of the response to the GOP letter. According to a report from Tehran Times, even Iranian Foreign Minister Mohammed Javad Zarif had a harsh reaction to letter, claiming that it lacked "legal validity" and showed that the Republican senators were "ignorant of international law."

"In our view, this letter has no legal validity and is just a propaganda scheme," Zarif said.

According to Fox News, Zarif argued that nuclear negotiations between the United States and Iran were still ongoing.

"It is very interesting that while negotiations are still in progress and while no agreement has been reached, some political pressure groups are so afraid even of the prospect of an agreement that they resort to unconventional methods, unprecedented in diplomatic history," Zarif said.

The Tehran Times described the contents of the letter sent by Cotton. Other signatories included potential 2016 presidential candidates and Sens. Marco Rubio, R-Fla., Ted Cruz, R-Texas, and Rand Paul, R-Ky.

"It has come to our attention while observing your nuclear negotiations with our government that you may not fully understand our constitutional system ... Anything not approved by Congress is a mere executive agreement," the senators wrote. "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."

According to Fox News, the vice president argued that Obama did not need congressional authority to make deals on the international stage. He cited three such examples, which included "diplomatic recognition of the People's Republic of China, the resolution of the Iran hostage crisis, and the conclusion of the Vietnam War."

"As the authors of this letter must know, the vast majority of our international commitments take effect without Congressional approval," Biden said.

Fox News reported that the U.S., alongside Britain, China, France, Germany and Russia, are negotiating an agreement with Tehran in regards to halting Iran's uranium enrichment program in exchange for lifting restrictions in a gradual manner. The negotiations are scheduled to resume in Switzerland next week.