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 CruzHow 'Big Pharma' stifles pharmaceutical innovation AIPAC must reach out to President Trump Under pressure, Dems hold back Gorsuch support MORE (R-Texas), Marco RubioMarco RubioSenators introduce new Iran sanctions Senate intel panel has not seen Nunes surveillance documents: lawmakers With no emerging leaders, no clear message, Democrats flounder MORE (R-Fla.) and Kelly AyotteKelly AyotteFEC commissioner to Trump: Prove voter fraud Live coverage: Day three of Supreme Court nominee hearing Lewandowski saw no evidence of voter fraud in New Hampshire MORE (R-N.H.), as well as prominent Democrats including Sens. Charles SchumerCharles SchumerDem to Trump: 'You truly are an evil man' Dem senator: GOP controls all of gov't, so success or failure is on them Trump tweets: We’ll put together a great plan after Obamacare explodes MORE (N.Y.), Kirsten GillibrandKirsten GillibrandSenators demand Pentagon action after nude photo scandal Chelsea Clinton to be honored by Variety, Lifetime Ten years later, House Dems reunite and look forward MORE (N.Y.) and Barbara MikulskiBarbara MikulskiAfter 30 years celebrating women’s history, have we made enough progress? DC restaurant owners sue Trump hotel over unfair competition: report Meet the Trump pick who could lead Russia probe 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.