WASHINGTON (AP) — Sen. Bernie Sanders is preparing several resolutions that would stop more than $20 billion in U.S. arms sales to Israel, a longshot effort but the most substantive pushback yet from Congress over the devastation in Gaza ahead of the first year anniversary of the Israel-Hamas war.

In a letter to Senate colleagues on Wednesday, Sanders said the U.S. cannot be “complicit in this humanitarian disaster.” The action would force an eventual vote to block the arms sales to Israel, though majority passage is highly unlikely.

“Much of this carnage in Gaza has been carried out with U.S.-provided military equipment,” Sanders, I-Vt., wrote.

As the war grinds toward a second year, and with the outcome of President Joe Biden’s efforts to broker a cease-fire deal and hostage release uncertain, the resolutions from Sanders would seek to reign in Israeli Prime Minister Benjamin Netanyahu’s assault on Gaza. The war has killed some 41,000 people in Gaza after the surprise Oct. 7 Hamas-led attack that killed about 1,200 people in Israel, and abducted 250 others, with militants still holding around 100 hostages.

While it’s doubtful the politically split Senate would pass the measures, the move is designed to send a message to the Netanyahu regime that its war effort is eroding the U.S.’s longtime bipartisan support for Israel. Sanders said he is working with other colleagues on the measures.

Key Senate Democrats have been pushing the Biden administration to end the Israel-Hamas war and lessen the humanitarian crisis, particularly in Gaza, where people’s homes, hospitals, schools and entire Palestinian families are being wiped out.

Sanders’ resolutions would halt sales of missile systems, tank rounds and other weaponry, some that has been singled out for causing some of the most severe destruction in Gaza, and new fighter jets. Congress had temporarily stalled some arms sales to Israel earlier this year, as lawmakers have tried to warn against the rising death toll.

Netanyahu was invited earlier this year to speak before the U.S. Congress, and he delivered a combative address that put the growing divide in the U.S. over his war effort on public display.

House Speaker Mike Johnson, a Republican, initiated the invitation to Netanyahu, but several Democrats boycotted the speech. Many top Democratic leaders spoke critically of the tone and content of Israeli prime minister’s address to Congress.

Under the Senate rules, once Sanders introduces the resolutions next week, he can force a vote almost instantly for consideration. The measures are being proposed as a joint resolution of disapproval of the arms sales, which is a mechanism that allows congressional oversight of foreign affairs.

Sanders said he would have some backing for his proposal. But it is not expected to have support from a majority, 51 votes, in the Senate to pass.

In the House, blocking the Israeli arms sales would face even tougher odds, where Republicans hold the majority, and have largely sided with Netanyahu’s approach to the war with Hamas.