Lawmakers are pressing President Obama to maintain tough sanctions against Iran as talks on Tehran's nuclear program begin Tuesday in Geneva.

House Foreign Affairs Committee Chairman Ed Royce, R-Calif., sent a letter to Obama on Monday arguing that a new round of sanctions are needed “to maximize our negotiating leverage.”

“International sanctions have forced Iran to the negotiating table; we should build upon this success with additional measures to compel Iran to make meaningful and lasting concessions,” Royce wrote.

Senate Foreign Relations Committee Ranking Member Bob Corker, R-Tenn., urged the Obama administration to keep sanctions in place and called for further measures to tighten the economic noose.

“Eagerness to exploit an opening with Iran should not lead to concessions before Iran takes verifiable steps to eliminate their nuclear weapons program,” he said. “Congress can play a constructive role by putting in place tough conditions on Iran before any easing of sanctions can occur.”

Congress generally has been united on Iran sanctions, with both Republicans and Democrats urging the administration to keep economic pressure on Tehran until it proves it is not developing nuclear weapons.

Newly-elected Iranian President Hassan Rouhani, who campaigned on promises to curb sanctions and boost his country's economy, reached out to the West and offered to allow more international scrutiny of Tehran's nuclear program in exchange for easing the crippling sanctions.

The House overwhelmingly approved stricter sanctions on Iran in July, but the Senate Banking Committee followed the Obama administration's advice to hold off on new sanctions to give Tehran time to prove its commitment to slowing its nuclear program and providing more transparency for international inspectors.

Shortly after Rouhani expressed willingness to curb his nuclear program, a group of six Democratic and four Republican senators wrote a letter saying they would consider suspending another round of sanctions but only if Tehran takes tangible steps to show the international community it is serious about slowing nuclear development.

The 10 senators said Tehran needs to comply with the International Atomic Energy Agency, the Nuclear Nonproliferation Treaty and all U.N. Security Council resolutions, which would require an immediate halt to enrichment.

Western nations point to Iran's enrichment program as evidence that it is trying to develop weapons, while Tehran insists it seeks nuclear energy for peaceful economic purposes.

Those signing the letter include Senate Foreign Relations Committee Chairman Robert Menendez, D-N.J., and fellow Sens. Chuck Schumer, D-N.Y., John McCain, R-Ariz., and Lindsey Graham, R-S.C.