US conservatives have condemned the nuclear deal reached between major world powers and Iran.
The agreement limits Iranian nuclear activity in return for removing of international economic sanctions.
The US Congress has 60 days to consider the deal and it will take some time before the sanctions are unpacked. There is a review period first during which no sanctions will be lifted.
President Obama has said he will veto any attempt to block it although he does need to keep members of his own party on board.
Republicans don't have enough votes to override the veto but are expected to appeal to sceptical Democrats, according to a BBC report.
The Republican Speaker of the US House of Representatives, John Boehner, said the deal would only "embolden" Tehran.
"Instead of stopping the spread of nuclear weapons in the Middle East, this deal is likely to fuel a nuclear arms race around the world," he added.
Lindsey Graham, a Republican senator and presidential candidate, described it as a "terrible" deal that would make matters worse.
Presidential Candidate Jeb Bush attacked the deal, saying: "This isn't diplomacy – it is appeasement."
He also condemned the Iranian regime: "The people of Iran, the region, Israel, America, and the world deserve better than a deal that consolidates the grip on power of the violent revolutionary clerics who rule Tehran with an iron fist."
Former Arkansas governor Mike Huckabee denounced the agreement. "Shame on the Obama administration for agreeing to a deal that empowers an evil Iranian regime to carry out its threat to 'wipe Israel off the map' and bring 'death to America'."
The so-called P5+1 want Iran to scale back its sensitive nuclear activities to guarantee that it cannot build a nuclear weapon. Iran, which wants international sanctions lifted, has always insisted that its nuclear work is peaceful.
Israeli Prime Minister Benjamin Netanyahu said that he did not regard Israel as being held to this agreement. "We will always defend ourselves," he added.