Tim Lenderking, the U.S. envoy for Yemen, said on Tuesday that the administration may fully reimpose a terrorism designation on the Houthis in Yemen if their attacks on commercial shipping in the Red Sea continue.

Lenderking, testifying before a subcommittee of the Senate Foreign Relations Committee, said that the U.S. may yet reimpose the Iran-backed militant group’s Foreign Terrorist Organization (FTO) designation, after imposing a separate label as a Specially Designated Terrorist Group (SDTG) last month. The FTO designation would grant additional authorities and penalties.

“I think we have come down hard with this designation that we have. The FTO is a possibility. We can constantly assess the impact of the campaign that we’re doing — both the military [and] the impact of the designation,” Lenderking said. “The SDTG… will cut off financial networks, their ability to fundraise. It will… hurt. And if we need to adjust to the FTO, if these attacks continue, then we’ll maintain that option.”

At the same time, he defended the administration’s early decision to rescind the FTO designation imposed at the end of the Trump administration, arguing that the U.S.’s diplomatic efforts to advance a peace process had seen success in advance of the current tensions.

Several senators on both sides of the aisle pressed Lenderking and Ambassador Daniel Shapiro, the deputy assistant secretary of defense for Middle East policy, on the legal authorities underpinning U.S. efforts to combat the Houthis, including both strikes on Houthi positions and ongoing efforts to patrol and protect maritime shipping lanes.

The senators argued that the military efforts were beyond the scope of existing U.S. law and the constitution, and required congressional authorization. Most of those who raised the issue indicated that they’d be supportive of providing such authorization, potentially subject to constraints including a limited time frame.

“If we believe this is a just military action, and I do, then we should authorize it,” Sen. Chris Murphy (D-CT), who chairs the subcommittee on the Near East, South Asia, Central Asia and Counterterrorism. “But we also need to acknowledge that there is a real risk of escalation, especially since Iran is unquestionably aiding the actions of the Houthis. Thus, an authorization is important to legalize the existing operations, but also guard against an unauthorized mission.”

Murphy said he and his colleagues would introduce legislation on the issue in the coming days. The committee’s chairman, Sen. Ben Cardin (D-MD) has previously supported calls for a congressional authorization.

Sen. Todd Young (R-IN), the subcommittee’s ranking member, indicated that he agreed that a war authorization should be passed, arguing that it “strengthens the hands of our commander-in-chief and our warfighters in re-establishing deterrence.” He also suggested that the U.S. should be taking more action against the Houthis and other Iranian proxies.

The administration officials insisted that the operations thus far fall within the scope of existing presidential authorities, but deferred many specific questions to legal experts. Lenderking said that, in addition to the U.S.’s military strikes and sanctions on the Houthis, the U.S. is seeking a diplomatic path to de-escalate the conflict with the Houthis.

Shapiro also said that it’s “hard to speculate” what military operation might ultimately convince the Houthis to stand down and cease their attacks.

Lawmakers pressed the officials on efforts to expand the international coalition — spearheaded by the U.S. and the United Kingdom — that has been working to counter the Houthis, asking specifically about China and Saudi Arabia.

“We do see a certain degree of freeloading [by China] that is absolutely unacceptable,” Lenderking said. “When we talk about an international problem that needs an international solution, we need the Chinese to be much more aggressive, much more aggressively engaged.”

He said the U.S. is engaging with the highest levels of the Chinese government on the subject.

Lenderking said that the U.S. is also engaging with partners in the region, adding that “certainly we need to see our Gulf partners in the game much more.” He noted that Egyptian commerce has been deeply impacted by the Houthi attacks.

Some lawmakers on the committee, including Sens. Tim Kaine (D-VA) and Chris Van Hollen (D-MD), suggested that the Houthis’ attacks would abate if the war in the Gaza Strip comes to a negotiated pause or conclusion, an idea that the administration officials seemed to question.

“The Houthis have made the claim that [the Gaza war] is the original motivation for their attacks. I think they’ve made some other claims along the way,” Shapiro said. “I would simply say that, whatever the rationale, or reason, or claim that the Houthis or any other organization would make for conducting these kinds of attacks, there’s no legitimacy to them.”

Shapiro also noted that attacks on shipping did not fully cease during a pause in the war last year, and that there “have been various points where they had spikes and valleys. So I don’t know to what we can attribute that.”

The two officials largely avoided questions about Iran’s oil smuggling activities, which have helped fund much of the proxy aggression across the region, stating that those issues fall under the purview of other agencies or other divisions. Shapiro, earlier in the hearing, had highlighted that the U.S. had intercepted Iranian arms shipments bound for the Houthis.

Shapiro, reiterating previous rhetoric from the administration, said that the U.S.’s strikes thus far against Iranian-backed forces in Iraq and Syria “demonstrated the administration’s willingness to directly hold Iran responsible for militia attacks” and that the U.S. “as necessary will continue to take military action against the [Islamic Revolutionary Guard Corps] and its affiliates.”

Shapiro, who briefly served as part of the team that attempted to re-negotiate a nuclear deal with Iran, also referred at one point to Rob Malley, the administration’s envoy for Iran, as “then-Special Envoy Malley.”

Malley has been suspended for months pending an investigation into his security clearance and potential mishandling of classified information, but the administration has not formally announced his dismissal. His X page continues to list him as “on leave from the State Department.”