In a notable test Tuesday, Sen. Bernie Sanders forced colleagues to decide whether to investigate human rights abuses in the Israel-Hamas war, a step toward potentially limiting U.S. military aid to Israel as its devastating attacks on Gaza grind past 100 days.

Senators overwhelmingly rejected the effort, a first of its kind tapping into a decades-old law that would require the State Department to, within 30 days, produce a report on whether the Israeli war effort in Gaza is violating human rights and international accords. If the administration failed to do so, U.S. military aid to Israel, long assured without question, could be quickly halted.

But the roll call vote begins to reveal the depth of unease among U.S. lawmakers over Israel’s prosecution of the war against Hamas. With no apparent end to the bombardment, Israel’s attacks against Palestinians, an attempt to root out Hamas leaders, are viewed by some as disproportional to the initial terrorist attack on Israel.

In all, 11 senators joined Sanders in the procedural vote, mostly Democrats from across the party’s spectrum, while 72 opposed.

“To my mind, Israel has the absolute right to defend itself from Hamas’ barbaric terrorist attack on October 7, no question about that,” Sanders told AP during an interview Monday ahead of the vote.

“But what Israel does not have a right to do — using military assistance from the United States — does not have the right to go to war against the entire Palestinian people,” said Sanders, the independent from Vermont. “And in my view, that’s what has been happening.”

The White House has rejected the approach from Sanders as “unworkable” as President Biden’s administration seeks a transition from Israel and works to ensure support at home and abroad against a stirring backlash to the scenes of destruction from Gaza.

Democratic Sen. Ben Cardin, the chairman of the Foreign Relations Committee, moved to table the measure, arguing it is “counterproductive” and would make it more difficult for the U.S. to prevent escalation of the expanding conflict.

“We do not believe that this resolution is the right vehicle to address these issues. And we don’t think now is the right time. It’s unworkable, quite frankly,” said a statement from the White House National Security Council’s John Kirby.

“The Israelis have indicated they are preparing to transition their operations to a much lower intensity. And we believe that transition will be helpful both in terms of reducing civilian casualties, as well as increasing humanitarian assistance,” Kirby said.

With repeated overtures to Israel Prime Minister Benjamin Netanyahu’s government, including shuttle diplomacy last week by U.S. Secretary of State Antony Blinken, the Biden administration is pushing Israel to shift the intensity of the battle. Some 24,000 people in Gaza, the majority of them women and children, have been killed, according to the territory’s Hamas-run Gaza Health Ministry, and the bombings have destroyed most of the housing units, displacing most of its 2.3 million people in a humanitarian catastrophe.

The Senate action comes as Biden’s request for $106 billion supplemental national security aid for Israel as well as Ukraine and other military needs is at a standstill. Republicans in Congress are insisting on attaching vast policy changes to stop the flow of immigration at the U.S.-Mexico border.

Of that supplemental aid package, more than $14 billion would go to Israel, including $10 billion in U.S. military assistance, as it retaliates against Hamas for the Oct. 7 surprise attack, among the most deadly assaults ever. Some 1,200 people were killed and 250 taken hostage, many still being held.

Several key Democratic senators have announced their unease with Israel’s war in Gaza, insisting the Biden administration must do more to push the Netanyahu government to reduce civilian casualties and improve living conditions for Palestinians in Gaza.

Going further, Sanders had already announced his refusal to support more military aid to Israel in the package because of the war.

“The time is now for the U.S. Senate to act,” Sanders said ahead of the vote, which he vowed was “just the beginning” of his efforts to limit the war’s devastation.

Heading toward the vote, Sanders said, what he’s trying to do is unprecedented in procedure, and essentially in practice.

“The Congress has always been supportive of Israel in general, and this begins to question the nature of the military campaign.” Sanders said.

The resolution is drawn from the Foreign Assistance Act of 1961, which was amended after the Nixon era, enabling Congress to provide oversight of U.S. military assistance abroad. It requires that any arms or military aid must be used in accordance with international human rights accords.

While senators have voted to try to halt foreign arms sales to other countries in the past, this is an untested mechanism.

The question before the Senate will be whether to ask the State Department for a report on whether human rights violations using U.S. equipment may have occurred during Israel’s current campaign against Gaza, according to Sanders’ office.

If the resolution were to be approved, it would force the State Department to produce a report of its findings within 30 days or risk the aid being cut off.