Schumer’s opposition could pave the way for more of Obama’s fellow Democrats to come out against the nuclear pact announced on July 1 between the United States, five other world powers and Iran.
The New York senator is among the most influential Jewish lawmakers in the US. He was the first Senate Democrat to announce his opposition to the agreement.
Another influential Jewish lawmaker, US Representative Eliot Engel, the top Democrat on the House of Representatives Foreign Affairs Committee, also said he would oppose the pact.
Israeli Prime Minister Benjamin Netanyahu has been pushing lawmakers to oppose the nuclear agreement, which he considers a threat to his country’s survival. Some pro-Israel groups have also been spending millions of dollars on an advertising campaign to push members of Congress to vote no.
Obama has been engaged in his own lobbying effort, including a combative speech on Wednesday in which he said abandoning the agreement would open up the prospect of war.
Speaking at a news conference on a visit to the Vietnamese capital Hanoi, US Secretary of State John Kerry, who negotiated the deal on the US side, said he respected Schumer and Engel but added that “rejection is not a policy for the future”.
“It does not offer any alternative and many people in arms control and others have actually pointed that out. While I completely respect everybody’s individual right to make a choice, I obviously disagree with the choice made,” he said.
Congress has until September 17 to consider a resolution of disapproval of the deal, which would eliminate Obama’s ability to waive all sanctions on Iran imposed by the Congress, a key component of the agreement.
Lawmakers will begin debating whether to reject the deal when they return from their recess on September 8.
Schumer insisted he was not influenced by party or politics and had not been pressured.
“Advocates on both sides have strong cases for their point of view that cannot simply be dismissed. This has made evaluating the agreement a difficult and deliberate endeavour, and after deep study, careful thought and considerable soul-searching, I have decided I must oppose the agreement and will vote yes on a motion of disapproval,” he said.
Obama has promised a veto if the resolution is passed by the House and Senate.
Republicans would need at least 13 Democrats in the Senate and 44 in the House to vote against Obama to muster the two-thirds majorities in both chambers needed to override a veto.