‘Anti-war groups on Friday are urging their supporters to pick up the phone to tell U.S. senators to back a joint resolution to “end America’s shameful role in Yemen.”

The Sanders-led resolution, introduced at the end of last month, calls for “the removal of United States Armed Forces from hostilities in the Republic of Yemen that have not been authorized by Congress.”

The United States has been fueling the conflict for years by aiding Saudi Arabia’s bombing campaign with weaponry and military intelligence, leading to accusations by rights groups and some lawmakers that the U.S. is complicit in fueling what the United Nations describes as “the world’s largest humanitarian crisis.”

There is urgency for constituents to make the calls, the groups warn, as a vote could come as soon as Monday.

In a further push to make the resolution successful, Win Without War led a group of over 50 organizationse—including CODEPINK, Democracy for America, Our Revolution, and War Resisters League—in sending a letter Thursday to senators calling on them to back the resolution.

Their letter says that “U.S. weapons sold to Saudi Arabia have been misused repeatedly in airstrikes on civilians and civilian objects, which are the leading cause of civilian casualties in the conflict and have destroyed Yemen’s vital infrastructure. This destruction of infrastructure has exacerbated the world’s largest hunger crisis in which 8.4 million civilians are on the brink of starvation and created the conditions necessary for the largest cholera outbreak ever documented in modern history,” they state.’

Read more: Senators Called on to End US Role in ‘Worst Humanitarian Crisis on the Planet’