76 senators sign letter demanding Obama take harder line against Iran

Seventy-six senators on Monday signed a letter demanding the Obama administration take a harder line to stop Iran’s nuclear program, including weighing possible military options. 

"We believe our nation must toughen sanctions and reinforce the credibility of our option to use military force at the same time as we fully explore a diplomatic solution to our dispute with Iran," read the letter sent to the White House.

The letter is signed by conservative lawmakers including Sens. Ted CruzTed CruzCruz lashes out at Murdoch and Ailes Cruz matches Trump in search interest ahead of Indiana Ron Paul: Cruz 'overemphasizes his religion' MORE (R-Texas), Marco RubioMarco RubioOvernight Healthcare: First House Republican backs Obama Zika request Time to wake-up to the Venezuelan Crisis First GOP rep backs Obama’s Zika funding request MORE (R-Fla.) and Kelly AyotteKelly AyotteHassan gets personal in first Senate ad GOP women push Trump on VP pick John Bolton PAC pours more cash into GOP campaigns MORE (R-N.H.), as well as prominent Democrats including Sens. Charles SchumerCharles SchumerCruz's dad: Trump 'would be worse than Hillary Clinton' With Ryan’s blessing, lawmakers press ahead with tax reform talks Big business will never appease the Left MORE (N.Y.), Kirsten GillibrandKirsten GillibrandCarter pledges probe of sex assault testimony This week: Congress on track to miss Puerto Rico deadline Maryland Senate primary intensifies MORE (N.Y.) and Barbara MikulskiBarbara MikulskiAcela primaries: Winners, losers Failed Md. gubernatorial candidate wins primary for Donna Edwards seat Candidate who spent M loses Md. House race MORE (Md.).

Lawmakers called on President Obama to "bring a renewed sense of urgency to the process.”

"Iran needs to understand that the time for diplomacy is nearing its end," they said. 

The letter comes as Hassan Rouhani was sworn in as Iran’s new president over the weekend. The White House on Sunday said the U.S. was willing to work with Iran, if the new leader engaged “substantively and seriously” on nuclear issues.

Congress, though, is working to enact tougher sanctions, with the House approving legislation last week to tighten controls against Iran's energy, shipping and insurance sectors.

Schumer last week said military action against Iran should never be taken off the table, but backed tightening sanctions as the preferred method to stop the country’s nuclear development.

“Ratcheting up the economic pressure against Iran is imperative,” he said last Wednesday on the Senate floor, “so that Iran sees it’s not in their best interests economically to continue on this path.”

The Pentagon has already drafted up plans for possible military action against Tehran, should the administration's strategy fail to stop Iran's nuclear program. 

However, Defense Department leaders continue to back the White House's approach of diplomatic and economic pressure to bring Tehran to heel. 

Iran’s regime insists its nuclear enrichment efforts are geared toward energy development, and not weaponization. 

Washington and its allies argue the Iranian program clearly puts the country on the path to developing nuclear arms.