WASHINGTON Sen. Chuck Schumer (D-N.Y.), the highest-ranking Democrat in the Senate, will vote to block President Donald Trumps plan to ship over $500 million of precision-guided munitions to Saudi Arabia, his office told HuffPost Monday.

Schumers decision makes him the most powerful supporter of a resolution of disapproval from Sens. Chris Murphy (D-Conn.), Al Franken (D-Minn.) and Rand Paul (R-Ky.) that is designed to show U.S. condemnation for the Saudis controversial role in a bloody civil war in Yemen.

I will support Senator Murphys resolution of disapproval. The human rights and humanitarian concerns have been well documented and are important, Schumer said Monday. Of equal concern to me is that the Saudi government continues to aid and abet terrorism via its relationship with [a hard-line school of Islam known as] Wahhabism and the funding of schools that spread extremist propaganda throughout the world.

Schumers announcement is the clearest sign yet that senators may successfully push back on the sale, after a failed attempt to block a U.S.-Saudi tank sale last fall. Schumer did not support that effort by Murphy and his partners. (In an email to HuffPost, an aide said that previous deal did not cover weapons to be used in Yemen.)

Two other top Democrats who opposed last years motion are also on board this year: Sens. Ben Cardin (D-Md.), the ranking member on the Senate Foreign Relations Committee, and Jack Reed (D-R.I.), the ranking member on the Senate Armed Services Committee.

The Obama administration initially approved the Saudi weapons transfer, but then put it on hold. Last month, Trump lifted the hold as part of a planned $110 billion package for Saudi Arabia. While the Trump administration can green-light such a shipment, senators also have an opportunity to vote to disapprove of it. If they do so, the deal would likely be delayed as the House considers whether to vote as well. Trump could eventually have to use his presidential veto to ensure the sale goes through.

General Democratic unity against the sale now seems likely. Its a win-win: a way for legislators to show opposition to Trump, who has pulled the Saudis close, and to burnish their humanitarian credentials.

The key for activists trying to pressure Saudi Arabia will now be convincing more red-state Democrats, like Sens. Joe Manchin (D-W.V.), Heidi Heitkamp (D-N.D.), and Claire McCaskill (D-Mo.), and Iran hawk Sen. Bob Menendez (D-N.J.) to join the cause. They also hope to win over some Republicans who have been willing to take stances on human rights issues, like Sens. Todd Young (R-Ind.) and Marco Rubio (R-Fla.)

Senators are expected to vote Tuesday afternoon on the resolution to disapprove of the sale, a congressional aide told HuffPost. Activists say even gaining one more vote than they did on last years motion would be a win because it would send a powerful signal to the Saudis. The U.S. relationship with the country rarely faces serious official criticism.

The resolution comes as the Saudis continue to fight in Yemen, where they and allies in a U.S.-backed coalition, including the United Arab Emirates, are responsible for thousands of civilian deaths and a worsening cholera outbreak.

All the while, the Saudis, the U.A.E. and others are isolating Qatar , a U.S. partner nation that hosts the biggest American base in the region. Tuesdays vote would give the Senate a rare chance to weigh in on the actions of the U.S.-dependent kingdom.