sessions shelby rsa

Sens. Jeff Sessions, left, and Richard Shelby, center, with Gov. Robert Bentley in a 2011 event at Redstone Arsenal. (AL.com file photo)

The hashtag #47traitors is trending on Twitter and a New York tabloid splashed the word "TRAITORS" across its front page on Tuesday morning as part of the fierce fallout from the U.S. Senate's letter to Iran.

Republicans in the Senate dispatched a letter Monday to Iranian leaders warning that any deal over nuclear weapons with President Obama might be voided as soon as he leaves office in January 2017. The letter is considered an effort by Senate leaders to have a voice in a long-term deal Obama is negotiating with Iran.

Alabama Sens. Richard Shelby and Jeff Sessions were among the 47 senators who signed the letter, authored by first-term Arkansas Sen. Tom Cotton.

"Senator Shelby joined his colleagues in sending the letter because he has serious concerns with the Obama Administration's ability to negotiate a viable deal with Iran regarding its nuclear program," Torrie Miller, Shelby's spokesman, said in an email Tuesday to AL.com.

The New York Daily News said on its front page Tuesday that Republicans are trying to sabotage the deal and ran photos of Sens. Mitch McConnell, Ted Cruz, Cotton and Rand Paul. All four signed the letter.

The Senate GOP’s letter to Iran has sparked American outrage and a #47Traitors Twitter trend. http://t.co/iNnoTLySm7 pic.twitter.com/JMnOresi9W — New York Daily News (@NYDailyNews) March 10, 2015

Vice President Joe Biden said in a statement Monday night that the letter was "beneath the dignity" of the Senate and "is expressly designed to undercut a sitting president in the midst of sensitive international negotiations," The Hill reported.

Obama also criticized the letter, The Washington Post reported. The president said Republican senators reaching out to the Iranian government was "an unusual coalition."

Iranian leaders dismissed the letter, describing it as a "propaganda ploy," The Hill reported.

On Tuesday morning, Cotton defended the letter, saying that Congress must be included for any deal to have a last effect.

"This letter is about stopping Iran from getting a nuclear deal," Cotton said on CNN.

Cotton said an Iranian government with a nuclear weapon is a dangerous prospect.

"We are the Constitutional backstop that our founding fathers created to ensure just this situation," he told CNN, "that you wouldn't have a single president committing the United States to a binding, lasting deal with the world's leading sponsor of state terrorism to get nuclear weapons - a regime that has been killing Americans for 35 years and extending its regional dominance to five capitals in the Middle East, all without a nuclear weapon. So imagine what they would do with a nuclear weapon."

Updated March 10, 2015, at 12:05 p.m. with comment from Shelby.