Updated

Despite President Obama’s nuclear deal with Iran that provides a gradual easing of decades of crippling economic sanctions, senators are fighting to renew a vital law that would preserve the sanctions option should Iran renege on its end of the bargain.

The Hill reports that senators plan to move soon on a proposal to extend what’s known as the Iran Sanctions Act, which is set to expire next year. Sen. Ben Cardin, D-Md., top Democrat on the Foreign Relations Committee, told the newspaper his colleagues have floated the possibility of tackling the issue in January or February.

But the debate could put the Obama administration in a tough spot.

Iran already is on high alert over any U.S. moves that could be perceived as a violation of the nuclear agreement – which trades sanctions relief for steps to roll back Iran’s nuclear program.

Iran surely would howl at any congressional attempts to keep broad sanctions legislation in force, even if specific sanctions are being lifted. But U.S. lawmakers say it’s vital for the U.S. to retain the leverage to re-trigger those sanctions if Iran cheats – and that would mean extending the sanctions law.

In a letter earlier this month to President Obama, Sen. Bob Menendez, D-N.J. – who along with Sen. Mark Kirk, R-Ill., introduced the Iran Sanctions Relief Oversight Act of 2015 -- warned that Iran will “continue to test the limits of international order.”

Their bill would extend the Iran Sanctions Act of 1996 for another decade.  In the letter to Obama, Menendez said that “lending” his support to the legislation would be a “good start.”

While facing congressional pressure to get tough on Iran, the Obama administration is working on a separate track to assuage Iran’s concerns over a separate set of visa restrictions approved by Congress.

That controversy stems from tightened security requirements for America’s visa waiver program, which allows citizens of 38 countries to travel to the U.S. without visas. Under changes in the newly signed spending bill, people from those countries who have traveled to Iran, Iraq, Syria and Sudan in the past five years must now obtain visas to enter the U.S.

Top Tehran officials complained the changes violate the terms of the nuclear deal, which says the U.S. and other world powers will refrain from any policy intended to adversely affect normalization of trade and economic relations with Iran.

In response, Secretary of State John Kerry assured the Iranian government that the changes will not interfere with the implementation of the nuclear deal, and suggested the administration could simply bypass the rules for Iran.

Kerry’s letter drew a rebuke from GOP lawmakers who accused the administration of trying to “placate” the regime.

Meanwhile, lawmakers from both parties have approached the administration with concerns about Iran’s compliance in the wake of Iran firing a medium-range ballistic missile in October, in apparent violation of U.N. sanctions. Iran also reportedly launched another ballistic missile in November.

Cardin and 20 other Democratic senators voiced concern about those tests – and the lack of action from the U.N. Security Council -- in a letter to Obama on Dec. 17.

The Associated Press contributed to this report.