Story highlights

Bipartisan proposal considers diplomatic effort under way around Iran nuclear issue

Legislation would give President Barack Obama more time to pursue diplomacy

Sanctions would kick in early if Iran violates current international nuclear deal

The Obama administration doesn't want sanctions bill; threatens veto

CNN  — 

Bipartisan legislation was introduced in the U.S. Senate on Thursday that would authorize new economic sanctions on Iran if it breaches an interim agreement to limit its nuclear program or fails to strike a final accord terminating those ambitions.

The proposal led by Foreign Relations Committee Chairman Robert Menendez, a New Jersey Democrat, and Mark Kirk, an Illinois Republican, emerged despite Obama administration appeals for Congress to defer pursuing new sanctions with diplomatic efforts ongoing.

The White House said new sanctions would undermine those delicate efforts on the global stage and President Barack Obama would veto the legislation if Congress were to approve it now.

A letter sent to Senate Majority Leader Harry Reid from nine Democratic committee chairs said international talks over Iran’s nuclear program should continue without additional sanctions being imposed by Congress.

“We believe that new sanctions would play into the hands of those in Iran who are most eager to see the negotiations fail,” the letter states.

But proponents of the plan that sprouted from bipartisan talks involving several lawmakers said the threat of stepped-up action could be a powerful lever against Iran’s nuclear interests and work toward more fruitful diplomacy.

“Current sanctions brought Iran to the negotiating table and a credible threat of future sanctions will require Iran to cooperate and act in good faith at the negotiating table,” Menendez said in a statement announcing the legislative effort.

Rep. Peter King, a New York Republican, told CNN’s The Situation Room that he would support the sanctions.

“The fact is that if Iran is serious about the agreement, they should have no problem with the sanctions because these sanctions only kick in if they don’t comply with the agreement,” he said. “Secondly, the President should want these sanctions as a weapon to hold over the Iranians, so I don’t see why the President is so opposed to these sanctions.”

A six-month agreement struck in November among the United States, other world powers and Iran calls for Tehran to start limiting its nuclear activities in return for a relaxation of sanctions that have crippled its economy.

Talks are under way on a permanent agreement, and the outcome is uncertain.

But the Senate proposal would give Obama more than a year to engage in further diplomacy before any new sanctions would kick in against Iran’s oil exports and other key areas of its economy.

Sanctions would hit sooner if Iran cheats on the interim deal or fails to reach a final accord.

Lawmakers demand a permanent global agreement that results in “termination of Iran’s nuclear weapons program” and prevents it from achieving such capability in the future.

The Obama administration has said the centerpiece of its policy is for Iran to not achieve a nuclear weapon.

The United States and other western powers believe Iran is attempting to build a bomb through uranium enrichment. But Tehran says its nuclear intentions are peaceful.

The proposal has the support of more than a quarter of the Senate.

The House approved a new Iran sanctions bill in July, well before the diplomatic effort yielded the interim agreement.

CNN’s Tom Cohen contributed to this report.