Washington CNN  — 

A key Senate Democrat is throwing his weight behind a proposal that would allow Congress to reject the Iran nuclear deal, complicating President Barack Obama’s efforts to dodge Republican opposition and lock in the pact on his own.

New York Sen. Chuck Schumer said Monday that he is backing legislation introduced by Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) to give Congress the ability to halt the implementation of the deal once the United States and five other world powers finalize the details in the coming months.

“This is a very serious issue that deserves careful consideration, and I expect to have a classified briefing in the near future. I strongly believe Congress should have the right to disapprove any agreement and I support the Corker bill which would allow that to occur,” Schumer told Politico on Monday.

Schumer’s endorsement is key, since he’s influential within his party and set to take over as the top Senate Democrat once Harry Reid departs at the end of next year.

With other Democrats now likely to follow suit, his position puts majority Republicans on track to gather the 60 votes they’ll need to advance Corker’s bill – and potentially a veto-proof majority, limiting Obama’s ability to get around that legislation.

The White House has complained that Corker’s bill, which would enable Congress to suspend the lifting of sanctions on Iran as part of the deal, could thwart negotiations that the United States, Britain, France, Germany, China and Russia are aiming to complete with Iran by June 30.

Democratic senators are expected to propose changes to the bill, which is set for a committee hearing next week. But it’s not clear whether the Obama administration would embrace any of those changes.

Obama told The New York Times in an interview published Sunday that “my hope is that we can find something that allows Congress to express itself but does not encroach on traditional presidential prerogatives – and ensures that, if in fact we get a good deal, that we can go ahead and implement it.”