The version of the annual defense policy bill being considered by the Senate this week includes a provision to limit U.S. military support to the Saudi Arabia-led coalition fighting in the Yemen civil war.

A bipartisan pair of senators behind the measure touted it on Thursday.

“The civil war and the world’s largest humanitarian crisis in Yemen are inflicting unacceptable damage to our national security interests and exacerbating heartbreaking human suffering,” Sens. Todd Young Todd Christopher YoungSenate GOP eyes early exit Why the US should rely more on strategy, not sanctions Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE (R-Ind.) and Jeanne Shaheen Cynthia (Jeanne) Jeanne ShaheenSenate Democrats introduce bill to sanction Russians over Taliban bounties Trump-backed candidate wins NH GOP Senate primary to take on Shaheen Democratic senator urges Trump to respond to Russian aggression MORE (D-N.H.) said in a joint statement. “The United States must use its influence to persuade Saudi Arabia and the United Arab Emirates to pursue an urgent diplomatic solution to end the civil war.”

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The Saudi-led coalition has been fighting Iran-backed Houthi rebels in Yemen since 2015. The United States supports the Saudi campaign with billions of dollars in arms sales, intelligence sharing and logistics such as air refueling.

But lawmakers in both chambers of Congress have grown increasingly frustrated as the civilian death toll rises, most of which has been blamed on Saudi airstrikes.

Earlier this year, the Senate blocked a resolution that would have ended U.S. military support to the campaign, though the vote margin was narrower than expected.

After that, Young and Shaheen introduced what they billed as a compromise proposal to require certification that the Saudi coalition is meeting certain criteria before the U.S. can refuel Saudi and coalition aircraft.

The proposal passed the Senate Foreign Relations Committee 14-7 last month and has now been folded into the National Defense Authorization Act.

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Under the provision, the secretary of State would have to certify to Congress that the Saudi coalition is undertaking efforts to end the civil war; alleviate the humanitarian disaster by increasing access to food, fuel and medicine; reduce delays in shipments of humanitarian supplies; and reduce the risk of harm to civilians.

Without the certification, the United States would be banned from refueling Saudi coalition aircraft for missions exclusively focused on the civil war. The United States could still refuel coalition aircraft for certain other missions, such as those against al Qaeda and the Islamic State in Iraq and Syria.

The secretary could also issue a waiver, including submitting a detailed justification to Congress, allowing the refueling for national security reasons.

On Thursday, Young and Shaheen also warned that an offensive on a key port in Yemen being considered by the coalition would be a mistake.

“The longer this war continues and the worse the humanitarian crisis grows, the more opportunities Tehran will have to undermine our interests in the region,” they said. “However, Saudi Arabia and the United Arab Emirates should understand that an attack on the port of Hudaydah — which is so vital to the prevention of famine in Yemen — would incite unprecedented additional opposition in Congress to Saudi-led coalition activities in Yemen.”