In a rare unanimous vote, the House of Representatives went on record Thursday opposing Iran’s choice for its representative at the United Nations on grounds that the would-be envoy participated in the 1979 takeover of the U.S. Embassy in Tehran.

The rising diplomatic furor over Iran’s selection of Hamid Aboutalebi forces the Obama administration to decide whether to block the ambassador from entry into the United States. Such a move is likely to cause a public spat with Tehran just as arms-control talks with Iran, which are a top priority for the White House, may be bearing fruit.

On Wednesday, the latest round of talks to limit Iran’s nuclear program ended on a markedly upbeat note, with U.S. and Iranian officials claiming progress and a willingness to move to a new, more intensive phase of negotiation over a written agreement when negotiators gather next month.

The Obama administration hinted Thursday that a confrontation over Aboutalebi could be avoided if Iran withdrew the nomination, but it did say whether President Obama will sign the legislation, which was also approved in the Senate, if Iran refuses. A veto could enrage lawmakers of both parties, while signing the legislation would anger Iran and possibly many other governments that would see Washington as acting inappropriately when it comes to access to the United Nations.

“Our preference certainly would have been that he wouldn’t have been nominated to begin with,” State Department spokeswoman Jen Psaki said. “We’ve made our concerns clear, and they’re going to make whatever choice they’ll make.”

The House voted Thursday to bar entry to the United States to those found to be engaged in espionage and terrorism or posing a threat to national security. The Senate has approved similar legislation, which would block Aboutalebi from entering New York, where the United Nations is headquartered.

“We’ve made clear and have communicated to the Iranians that the selection they’ve put forward is not viable,” White House press secretary Jay Carney said.

Sen. Ted Cruz (R-Tex.), who introduced the legislation in the Senate, urged Obama to sign the bill.

“We, as a country, can send an unequivocal message to rogue nations like Iran that the United States will not tolerate this kind of provocative and hostile behavior,” Cruz said.

Fifty-two Americans were held for 444 days at the beginning of Iran’s 1979 Islamic revolution, which replaced a pro-American government leadership with a vehemently anti-American leadership.

Iran maintains a large and active mission to the United Nations, despite 35 years of diplomatic estrangement from the United States. Iranian diplomats are confined to New York, but in keeping with long-standing practice as the U.N. host country, the United States routinely approves diplomatic passage for Iranian diplomats and leaders.

Aboutalebi has said he was not part of the takeover and only provided translation services later. The government of Iranian President Hassan Rouhani has said it stands by its nominee, without discussing any involvement in the events in 1979.

On Wednesday, Iran’s foreign minister, Mohammad Javad Zarif, said blocking Aboutalebi from setting foot on U.S. soil would be “unacceptable.” Foreign Ministry spokeswoman Marzieh Afkham added that Aboutalebi “is the choice of the Islamic Republic of Iran for representing the country in the U.N., and he is one of Iran’s most qualified diplomats.”

State-controlled and state-linked Iranian news media were filled this week with outrage that Washington could block the veteran diplomat, who has held postings around the world, including as Iran’s representative to the European Union.

At the same time, critics outside Iran are warning Washington that blocking Aboutalebi could call into question the role of the United States as host country, as well as other host-country agreements for international organizations around the world.

Iranian negotiators have avoided allowing matters not directly tied to the nuclear issue to derail the process, and despite the emotional high stakes, the Aboutalebi issue is not likely to do so either.

“We believe three months is enough to reach a final deal provided that all sides enter negotiations with goodwill,” Zarif told reporters at the conclusion of the latest round of talks in Vienna. He predicted that a deal could be made in July but also said that taking more time would not “be a disaster.”

Ayatollah Ali Khamenei, Iran’s supreme leader and a longtime skeptic of the ongoing talks, also reiterated his support for them.

“The talks should continue, but despite the continuation of negotiations, everyone should know that Iran’s activities in nuclear research and development, as well as its nuclear achievements, will never be stopped,” Khamenei, Iran’s ultimate decision-maker, said at a gathering of nuclear scientists in Tehran on Wednesday.

Rezaian reported from Tehran.