House Minority Leader Nancy Pelosi on Wednesday announced she will oppose legislation empowering Congress to review the White House’s nuclear deal with Iran.

The California Democrat said the proposal, sponsored by Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.), threatens to sink the agreement at a crucial juncture in the talks.

She’s urging lawmakers oppose the measure in order to allow negotiators the space to hash out the final details ahead of the June 30 deadline.