U.S. senators are attempting to block the State Department’s deal to sell Saudi Arabia nearly $1.5 billion in weapons, just days after the move was announced by the Obama administration.

Sen. Rand Paul (R-Ky.) told Foreign Policy that he would “work with a bipartisan coalition to explore forcing a vote on blocking this sale. Saudi Arabia is an unreliable ally with a poor human rights record. We should not rush to sell them advanced arms and promote an arms race in the Middle East.”

Congressional opposition to the arms sale came as the Saudi-led, U.S.-backed military coalition broke an unsteady five-month ceasefire in Yemen last week and resumed bombing in the capital city of Sana’a—prompting immediate reports of civilian deaths. On Saturday, Doctors Without Borders/Médecins Sans Frontières (MSF) reported that an airstrike on a school in northern Yemen killed 10 children and wounded 28 others.

Paul and Sen. Chris Murphy (D-Conn.), both of whom sit on the Foreign Relations Committee, are outspoken critics of the coalition.

“If you talk to Yemeni Americans, they will tell you in Yemen this isn’t a Saudi bombing campaign, it’s a U.S. bombing campaign,” Murphy said in June. “Every single civilian death inside Yemen is attributable to the United States.”