Vermont Democratic Senator Patrick Leahy on Sunday criticized fellow progressives pushing for new Iran sanctions while the Obama administration and other U.S. allies try to curtail the Middle Eastern nation's nuclear ambitions.

“I think that's a mistake,” Leahy, chairman of the Senate Judiciary Committee, said on “Fox News Sunday.”

“I think if we do that we screw up the ability to have real negotiations,” Leahy added.

A six-month deal between the P5+1 nations and Iran is set to go into effect Monday. The accord loosens economic sanctions on Iran in exchange for the nation cutting back on certain elements of its nuclear arsenal.

However, Republicans — and a growing number of Democrats — say the U.S. should codify new sanctions in case the deal falls through.

President Obama last week met with Senate Democrats at the White House in an attempt to convince them to put sanctions on hold. But some Republicans say Obama may have to ultimately veto an Iran sanctions bill, with a handful of Democrats expected to support GOP efforts.