The US Senate has passed a bill that, when passed by the House of Representatives, requires Congressional approval for any agreement with regard to the waiver of the US Iran sanctions program.
At the moment, President Obama has the power to unilaterally waive US sanctions. However, under the new legislation any such decision would be subject to a 30 day Congressional review period and Congress would then be able to enact a joint resolution supporting or opposing the President’s decision, or to take no action. If Congress opposes the agreement, the President may invoke his right to veto the resolution still, which then would be subject to a 2/3 vote to override it in Congress. If such vote were to successfully override the President’s veto, the joint resolution would prohibit President Obama from lifting the sanctions.
What the consequences are of the Iran Nuclear Agreement Review Act for the Iran Nuclear Framework Agreement is yet uncertain. The adoption of this bill could prove to be an obstacle in the ongoing negotiations between the US and Iran, whilst Iran has already indicated that Iran insists on a full and immediate relief of all sanctions opposed against it. This could lead to the contrasting situation in which UN or EU sanctions would be lifted, but US sanctions would remain in force.
The Iran Nuclear Agreement Review Act is at: https://www.congress.gov/bill/114th-congress/house-bill/1191