More than a dozen Senate Democrats said Tuesday that they will seek to block President Joe Biden’s request to skirt congressional oversight of arms transfers to Israel, the latest signal of frustration among members of his own political party who have recoiled at the stunning civilian death toll resulting from Israel’s offensive in Gaza.

Led by Sen. Tim Kaine (D-Va.), the push comes as more Democrats, historically stalwart backers of the Jewish state, have urged the president to step up efforts to rein in America’s chief ally in the Middle East. International human rights groups have accused Israel of conducting indiscriminate bombing in Gaza amounting to war crimes.

Nearly 23,000 Palestinians have been killed in the past three months of fighting in the densely populated enclave, according to Gaza health officials, as Israel wages a devastating campaign in retaliation for the cross-border attack by Hamas militants that left 1,200 dead.

The Biden administration, which rushed to back Israel after Hamas’s Oct. 7 massacre, has been unusually secretive about its ongoing military support program, and is seeking to exempt its arms transfers from a mandatory congressional notification process that applies to all other foreign arms sales.

Administration officials already bypassed Congress in that regard late last month, angering Democrats by invoking an emergency authority and the “urgency of Israel’s defensive needs” to approve a $147.5 million sale of artillery rounds and related equipment.

At the moment, lawmakers are negotiating over Biden’s request for more than $10 billion in additional military assistance for Israel — already the largest recipient of U.S. security aid — as part of a $106 billion supplemental budget request that would pay for a host of national security initiatives. The proposal also would provide billions of dollars for U.S. border security, as well as military assistance for Ukraine and Taiwan, but remains stalled as Republicans and Democrats search for an agreement on immigration reforms targeting illegal crossings at the U.S. southern border.

Biden’s request, according to bill text released by the Senate Appropriations Committee, included a provision saying “any congressional notification requirement applicable to funds made available ... for Israel may be waived if the Secretary of State determines that to do so is in the national security interest of the United States.”

Kaine and his fellow Senate Democrats — Martin Heinrich (N.M.), Chris Van Hollen (Md.), Jeff Merkley (Ore.), Elizabeth Warren (Mass.), Peter Welch (Vt.), Ben Ray Luján (N.M.), Dick Durbin (Ill.), Brian Schatz (Hawaii), Jeanne Shaheen (N.H.), Raphael G. Warnock (Ga.), Tom Carper (Del.) and Chris Murphy (Conn.) — said their amendment would strike that provision.

“I have strongly supported U.S. aid necessary for Israel’s defense,” Kaine said in a statement, “but all nations should be subject to the same standard.” The statement stops short of condemning the Israeli offensive or making other demands of the administration to restrain Israel.

Other Democrats in the House and Senate have been far more critical, calling on the administration to force Israel to meet certain conditions to receive U.S. aid or openly opposing any further assistance. The Democratic Party’s left flank has been particularly vocal in urging Biden to take a stronger stance in support of Palestinian human rights.

Sen. Bernie Sanders (I-Vt.) said last week that he opposes the administration’s additional aid request for Israel, calling the campaign in Gaza “grossly disproportionate, immoral, and in violation of international law.”

“And, most importantly for Americans, we must understand that Israel’s war against the Palestinian people has been significantly waged with U.S. bombs, artillery shells, and other forms of weaponry,” Sanders said in a statement.

A number of other lawmakers have called for the administration to impose conditions on American weapons transfers.

The administration’s lack of transparency also has prompted Democrats in Congress to demand basic information about its assistance to Israel, and the parameters of Israel’s goals, methods and process for measuring success in Gaza. Critics have drawn comparisons to Biden’s approach in aiding Ukraine, which the administration says also faces a dire need for more weaponry in its fight against Russia. Since the war there began two years ago, the State Department and Pentagon have publicly documented tens of billions of dollars in U.S. assistance.