U.S. Sen. Chuck Schumer, a high ranking New York Democrat, announced he will vote against President Barack Obama's historic nuclear deal with Iran.

Schumer, an influential Jewish senator who's poised to assume leadership of his party in 2017, said on Thursday that he will not support the U.S.-Iran nuclear deal, which Obama announced last month. Under the agreement, the U.S., Russia, China, the U.K., France and Germany agreed to lift Iran's economic sanctions while the Islamic republic vowed to limit its nuclear program for the next 10 years.

Schumer, however, says he will not approve the resolution because he believes that Iran will continue to build a nuclear weapon regardless of the deal.

"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," Schumer wrote in an article posted on Medium.

"I will vote to disapprove the agreement, not because I believe war is a viable or desirable option, nor to challenge the path of diplomacy. It is because I believe Iran will not change, and under this agreement it will be able to achieve its dual goals of eliminating sanctions while ultimately retaining its nuclear and non-nuclear power."

According to his aide, Schumer would also vote to override the president's veto on the deal, reports CNN.

Proponents of the deal blasted Schumer following his announcement.

"Chuck Schumer, who said it was a mistake to pass Obamacare, now comes out again the Iran Deal. This is our next Senate leader?" tweeted former speechwriter for Obamam Jon Favreau.

Although Schumer's opposition to the deal comes as a major blow to the Obama administration, supporters are optimistic that there will still be enough support to pass it.

"I wouldn't underestimate the importance of Chuck Schumer, but he's not likely to reverse the situation," Rep. David E. Price, D-N.C., said of Schumer's announcement, according to the New York Times.

The majority of Republican leaders in the House and Senate have also promised to disapprove the nuclear deal when the resolution is presented for a vote in mid-September. However, Obama has launched a massive lobbying effort to persuade lawmakers to support the July 14 agreement.