The U.S. Senate is expected to vote on May 7 on a proposal by Republican lawmakers that would give Congress the power to review an international nuclear agreement with Iran currently being negotiated by six world powers.
The bill aims to give the U.S. Congress authority to impose tougher conditions on Tehran.
Should a deal with Tehran be reached, the bill would freeze U.S. sanctions relief for Iran for 30 days, during which time Congress could vote to approve or disapprove the accord.
Tehran has criticized the so-called Iran Nuclear Review Act, saying that Iranian negotiators are working with six world powers on a permanent nuclear agreement -- not legislators from any single contry.
A dispute arose last week among Republican senators about amendments added to the bill.
Many of the provisions were considered so-called "poison pills" that would cause some Democrats to withdraw their support and provoke a veto by President Barack Obama.