The House version of the nearly $700 billion 2018 National Defense Authorization Act (NDAA) includes multiple amendments aimed at limiting US involvement in the Saudi War in Yemen, explicitly forbidding the deployment of ground troops there, or spending any money on military operations outside the scope of the 2001 AUMF.
The Nolan Amendment prohibits the deployment of troops to participate in any way in the war, which is seen not only as restricting ground troops being sent to Yemen to fight on the side of the Saudis, but also appears aimed at limiting mid-air refueling operations for Saudi warplanes.
The Lieu Amendment requires a report from the State Department and the Pentagon on whether or not the Saudis are complying with the US-provided “No Strike List” for Yemen, as well as their improvement of targeting capabilities to avoid hitting civilians.
Finally, the Davidson Amendment prohibits all US military action in Yemen that is outside of the scope of the 2001 AUMF. This would preclude operations against the Shi’ite Houthis, who obviously were nothing to do with 9/11, though it would not restrict US operations against al-Qaeda forces inside Yemen.
All of these amendments would still have to survive reconciliation between the House and Senate versions, with the Senate usually more reluctant to place such limits in the military spending bills. It also isn’t clear if the administration would comply with the limits.
That’s mostly because the 2001 AUMF has been broadly interpreted far beyond al-Qaeda and 9/11 by administrations, claiming instead that anything they attach the word “terror” to is authorized. The Nolan Amendment doesn’t include the AUMF exemption, which likely means its more likely to get stripped from the bill.