More than 170,000 Americans have signed a petition condemning Jewish Senator Charles Schumer’s open hostility towards the Iran nuclear agreement.

In a major break with the White House, Senator Schumer from New York announced on Thursday that he would vote against the conclusion of nuclear talks reached between Iran and the P5+1 group – the US, Britain, France, China, Russia and Germany – last month in Vienna, Austria.

“New York Senator Chuck Schumer just publicly declared that he will vote to kill the historic Iran nuclear peace deal and urge other Democrats in the Senate to do the same,” says the petition, issued by CREDO Action.

Credo Action calls itself a “social change organization that supports activism and funds progressive nonprofits.” The progressive organization has a goal of 200,000 signatures.

“There’s no excuse for any Democrat to oppose the deal — least of all Senator Schumer, who is in line to take over leadership of the Senate Democrats once Senator Harry Reid retires,” adds the petition, which was launched on Saturday.

“Chuck Schumer was wrong on Iraq when he voted for war and he is wrong on Iran,” the petition continues. “Schumer’s decision to join Republicans in attempting to sabotage the Iran nuclear deal once again shows that he is unfit to lead Senate Democrats.”

The Republican-dominated Congress is reviewing the Iran nuclear agreement and is likely to vote on it next month.

Under legislation President Barack Obama signed in May, Congress has until September 17 to review and vote to either approve or disapprove of the Joint Comprehensive Plan of Action announced by Iran and the P5+1 group of countries on July 14.

Most Republicans oppose the nuclear agreement, but they need a two-thirds vote in both chambers of Congress to override a presidential veto, and to reach that threshold, Republicans need Democratic support.

Moments after Schumer’s announcement, Representative Eliot Engel, the ranking Democrat on the House Foreign Affairs Committee, also declared that he would join Obama’s rivals to oppose the nuclear accord.

The decisions by Schumer and Engel are considered a blow to Obama, who is striving to save the Iran nuclear agreement in Congress, which is expected to pass a resolution opposing the measure.