A letter drafted by Reps. Jesse Jackson Jr. (D-Ill.) and Mike Pence (R-Ind.) urging swift, tough sanctions on Iran will be mailed to President Barack ObamaBarack Hussein ObamaStephen Sondheim, legendary Broadway songwriter, dies at 91 With extreme gerrymanders locking in, Biden needs to make democracy preservation job one Republicans seem set to win the midterms — unless they defeat themselves MORE on Monday with 366 House signatures.

Late Friday afternoon, Jackson's office said they were still in the process of gathering the hundreds of signatures on the letter.

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"Mr. President, you have stated this issue is a priority for your administration. You have attempted to engage the Iranian regime for over a year. You have gone to the United Nations Security Council in an effort to impose tough new sanctions on Iran. But time is not on our side," the letter states.

"We cannot allow those who would oppose or delay sanctions to govern either the timing or content of our efforts," it says, in reference to the lack of support at the Security Council by veto-wielders China and Russia.

The letter calls on Obama to "fulfill your June 2008 pledge that you would do 'everything in my power to prevent Iran from obtaining a nuclear weapon,'" to "rapidly" implement the sanctions legislation when it comes out of conference and use whatever presidential powers at his means to impose "punishing measures" on Tehran.

Jackson and Pence, along with Majority Leader Steny Hoyer (D-Md.) and Minority Whip Eric CantorEric Ivan CantorRepublicans eager to take on Spanberger in Virginia Virginia emerging as ground zero in battle for House majority McAuliffe's loss exposes deepening Democratic rift MORE (R-Va.), as well as Reps. Ileana Ros-Lehtinen (R-Fla.) and Dan Burton (R-Ind.), confirmed the culmination of their effort at a Wednesday afternoon press conference.

"This is a moment where traditional loyalties and interests give way to the interests of the United States of America," said Pence, who characterized the letter to Obama as "firm but respectful."

In the Senate, a similar letter circulated by Sens. Charles SchumerChuck SchumerSchumer mourns death of 'amazing' father Feehery: The honest contrarian Biden administration to release oil from strategic reserve: reports MORE (D-N.Y.) and Lindsey GrahamLindsey Olin GrahamGraham emerges as go-to ally for Biden's judicial picks This Thanksgiving, skip the political food fights and talk UFOs instead Biden move to tap oil reserves draws GOP pushback MORE (R-S.C.) had gathered 76 signatures as of Wednesday, but that number had climbed to 80 as of Friday.

"Preventing Iran from obtaining nuclear weapons remains a diplomatic imperative," the letter states. "But time is not on the side of those who seek to prevent a nuclear Iran.

"... We urge you to move quickly to implement your existing authority on Iran and the legislation we send you, and to galvanize the international community to take immediate, substantive steps. Now is the time for action focused on preventing a nuclear Iran. We look forward to working with you on this important task."

In December, the House approved 412-12 a measure enabling Obama to ban foreign firms that supply Iran with refined petroleum from doing business in the U.S. The Senate passed its own version of sanctions targeting Iran's energy sector by voice vote on Jan. 28.

Next week, the House will move to instruct conferees and take the sanctions bill to conference.