The American liberal activist group and political action committee MoveOn is launching a “Democratic Party donor strike” over Sen. Charles Schumer’s decision to oppose the Iran nuclear agreement.

As part of the strike, the 8-million-member group will withhold contributions from the Democratic Senatorial Campaign Committee and from any Democratic candidate who succeeds in undermining the nuclear accord with Iran.

“Our goal will be to secure commitments to withhold $10 million in contributions within 72 hours after this campaign launches,” MoveOn political action executive director Ilya Sheyman said in a statement.

In a major break with the White House, Senator Schumer of New York announced Thursday that he would vote against the nuclear agreement with Iran.

“While not unexpected, it is outrageous and unacceptable that the Democrat who wants to be the party’s leader in the Senate is siding with the Republican partisans and neoconservative ideologues who are trying to scrap this agreement and put us on the path to war,” Sheyman said of Schumer, who is next in line to be the Senate’s top Democrat,

“No real Democratic leader does this,” he added. “If this is what counts as ‘leadership’ among Democrats in the Senate, Senate Democrats should be prepared to find a new leader or few followers.”

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.

US Secretary of State John Kerry (L) and committee ranking member Rep. Eliot Engel speak while a protester stands before a hearing of the House Foreign Affairs Committee on Capitol Hill on February 25, 2015 in Washington, DC. (AFP photo)

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 sell the Iran accord to Congress.