The bill, sponsored by Sens. Mark Kirk (R-Ill.) and Robert Menendez (D-N.J.), is backed by much of the pro-Israel community, led by the American Israel Public Affairs Committee. The U.S. House of Representatives last summer overwhelmingly approved a similar sanctions package.

The Senate bill’s backers say it gives the United States greater leverage in its efforts to negotiate a resolution to the standoff over Iran’s nuclear program. But President Obama says new sanctions could scuttle the talks.

Two of the bill’s most controversial provisions are a requirement that Iran not be allowed to maintain any uranium enrichment capacity and non-binding language calling on the United States to support Israel if it strikes Iran’s nuclear program in self-defense.

The Nuclear Weapon Free Iran Act of 2013 was introduced in the Senate on Dec. 20 and so far has garnered 59 co-sponsors, eight short of the two-thirds necessary to override a promised presidential veto. The bill enjoys the overwhelming support of Republicans, with only two GOP senators not among the co-sponsors. In addition to Menendez, 15 other Democrats have signed on as co-sponsors — although one of these, Sen. Richard Blumenthal (D-Conn.), now says there “may not need to be a vote” as long as progress is being made in talks.

At least 20 members of the Senate’s Democratic caucus have come out in recent days supporting the White House in its bid to keep the sanctions bill from advancing.

White House officials have said in off-the-record conversations with Jewish leaders that the sanctions themselves are not controversial. Should the talks with Iran fail, officials have said that they would press to have Congress pass the new sanctions “in a day.”

What are the new sanctions?

–Existing sanctions on Iranian crude oil would be expanded to include its refined version, petroleum, and its products.

–Existing sanctions on Iran’s shipping sector would also be expanded to include engineering, mining and construction sectors, as well as Iranian free economic zones.

–Existing sanctions on Iran’s financial sector would be broadened beyond current bans on its nuclear and energy sectors to virtually any dealings, save for humanitarian transactions.

–The bill also expands individuals targeted by sanctions to include employees of a broad selection of official and semi-official Iranian bodies.

Disagreement over timing

The White House’s principal objection to the bill is its timing. The Joint Plan of Action, the November interim agreement between Iran and six major powers, is intended to create a six-month window for reaching a final settlement. The interim agreement, which exchanged a partial rollback of existing sanctions for a partial rollback of Iran’s nuclear activity, requires the United States to “refrain from imposing new nuclear-related sanctions.”

It’s unclear whether the legislation as currently devised violates those terms. Backers of the bill say that by allowing the president to suspend implementation for six months, the legislation does not violate the interim deal. “It provides the president the time he has requested to see if negotiations can succeed without additional sanctions being imposed during the talks if Iran keeps to its end of the interim framework agreement,” Brad Gordon, the director of policy and government affairs for AIPAC, says in a video message posted on the group’s website.

But others argue that mere enactment of the bill, even if implementation is delayed, constitutes a violation. “This bill would impose new sanctions and, while the measures may not be enforced, they will become law,” says an analysis by the Arms Control Association.

The White House has also warned that while the passage of new sanctions legislation might not spur Iran to quit the talks, as it has threatened to do, they might lead to the collapse of the international coalition that brought Iran to the table.

Disagreement over outcome

Another White House objection has to do with outcomes required by the bill. The Obama administration complains that the bill would constrain its ability to negotiate an agreement with the Iranians. Backers of the bill admit as much.

“The Nuclear Weapons Free Iran Act of 2013 clearly defines parameters for a final agreement,” Gordon says in the AIPAC video.

The most contentious of the requirements has to do with uranium enrichment. For the president to suspend the legislation’s sanctions provisions, the bill requires he must certify that a final agreement will “dismantle Iran’s illicit nuclear infrastructure, including enrichment and reprocessing capabilities and facilities.”

Such a requirement comports with the demand of Israeli Prime Minister Benjamin Netanyahu that any final agreement permanently end Iran’s enrichment capability. Iranian nuclear knowledge and capability is advanced enough, according to supporters of this condition, that even enriching uranium to five percent — a level generally used for peaceful purposes — would allow Iran to quickly advance to weapons-grade enrichment if it so decided.

White House officials have said that Iran would never accept a total enrichment ban and that the best possible outcome would be a five percent enrichment capability.

The bill would also allow Congress, by a vote of both chambers, to reimpose any sanctions that were suspended as a result of an agreement.

Disagreement over Israel

The bill recommends U.S. backing for Israel should it determine that it must strike Iran. In its “sense of Congress” section, it says:  “If the Government of Israel is compelled to take military action in legitimate self-defense against Iran’s nuclear weapon program, the United States Government should stand with Israel and provide, in accordance with the law of the United States and the constitutional responsibility of Congress to authorize the use of military force, diplomatic, military, and economic support to the Government of Israel in its defense of its territory, people, and existence.”

That language, according to critics, amounts to allowing a foreign nation — albeit one that is a close ally — a determinative role in deciding when the United States joins a military action.

“Let me acknowledge Israel’s real, well-founded concerns that a nuclear-armed Iran would threaten its very existence,” Sen. Dianne Feinstein (D-Calif.), the chairwoman of the Senate Intelligence Committee, said in a Jan. 14 floor speech opposing the bill. “While I recognize and share Israel’s concern, we cannot let Israel determine when and where the U.S. goes to war. By stating that the U.S. should provide military support to Israel should it attack Iran, I fear that is exactly what this bill will do.”

The bill’s backers note that by definition, “sense of Congress” language is not binding and that the bill concludes that nothing in it “shall be construed as a declaration of war or an authorization of the use of force against Iran.”

Moreover, they note, the language is identical to a non-binding resolution that the Senate passed in May by a vote 99 to 0. Feinstein was among its co-sponsors.

Ron Kampeas is JTA’s Washington bureau chief, responsible for coordinating coverage in the U.S. capital and analyzing political developments that affect the Jewish world. He comes to JTA from The Associated Press, where he worked for more than a decade in its bureaus in Jerusalem, New York, London and, most recently, Washington. He has reported from Northern Ireland, Afghanistan, Bosnia and West Africa. While living in Israel, he also worked for the Jerusalem Post and several Jewish organizations.