Republicans claim to have enough votes to pass a resolution blocking the Iran nuclear deal in the U.S. House, but not enough to overcome a likely presidential veto of their resolution.
House Republican Peter Roskam said that 218 of the House's 434 current members have committed to voting for his resolution of a disapproval -- all of them Republican.
A vote on the resolution is expected September 17.
However, a two-thirds majority of 290 votes would be needed to overcome a presidential veto.
House Minority Leader Nancy Pelosi has said she expects enough Democrats will vote in favor of the deal to sustain a veto.
While a smattering of Democrats has come out in favor of the deal, many remain uncommitted. President Barack Obama said last week that many are cowed by the powerful lobbying forces arrayed against the deal.
"Time is not the friend of this deal," Roskam said. "The more time members spend evaluating this agreement, the more they realize it's an historic mistake."