A senior Democratic senator has blocked a Trump administration proposed rule to switch oversight authority of firearm sales abroad from the State Department to the Commerce Department, arguing the move would significantly weaken congressional oversight and increase the risk of terrorists and criminals getting their hands on powerful military-grade weapons.

Sen. Robert Menendez, ranking member on the Foreign Relations Committee, placed the hold last week after he was notified earlier this month about the proposed change by the State Department. Menendez is objecting to the final language of the rule.

“Firearms and ammunition — especially those derived from military models … are uniquely dangerous,” the New Jersey Democrat wrote in a Feb. 22 letter to Secretary of State Mike Pompeo announcing his hold. “They should be subject to more, not less, rigorous export controls and oversight.”

Hill staffers and outside experts are concerned President Donald Trump will disregard Menendez’s hold, which is not legally binding but is based on decades of bipartisan tradition. The development of the rule change started under the Obama administration, and the Trump administration is now proposing it.

The proposed rule change would switch oversight responsibility on exports of firearms, including semi-automatic pistols, sniper rifles and AK-47-type assault weapons from Foggy Bottom to the Commerce Department. Critics of the move say that human rights, terrorism and rule of law concerns would take a back seat when considering an export request. It would also, they say, make it more difficult for lawmakers to learn about and stop firearm sales they disagree with.