Sen. Chuck Schumer (D-N.Y.) announced Thursday night that he will not support President Barack Obama's nuclear deal with Iran, furthering the division among politicians on the issue.

"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 said in a blog post, according to CNN.

"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," Schumer said. "It is because I believe Iran will not change."

The Iran deal has sparked hot political debate recently, and now Schumer is straying from traditional party lines. If he follows through on his vow, he'll be voting along with Republicans against the deal engineered by Democrat President Barack Obama.

"Chuck Schumer, who said it was a mistake to pass Obamacare, now comes out against the Iran Deal. This is our next Senate leader?" Jon Favreau, former speechwriter, said in a tweet. Several Democrats have come forward to say they will back the deal, which will be voted upon in September, CNN reported.

Sen. Bernie Sanders (I-Vt.), who is running for President in the Democratic primary, has said he will back the deal, according to the Times-Union. "The test of a great nation is not how many wars it can engage in, but how it can resolve international conflicts in a peaceful manner," Sanders said.

Schumer is expected to be the next Democratic leader in the Senate, according to The Wall Street Journal. Five Democrats in the House have said they will likewise not support the deal. The Iran Deal puts limits on Iran's nuclear program. In return, sanctions against Iran will be lifted. Schumer is the first Democrat in the Senate to publicly oppose the deal.