Sen. Ed Markey (D-Mass.) is threatening to stall a top State Department nominee until the Trump administration reverses course on allowing blueprints for 3D printed guns to be published online.

Markey said during a Foreign Relations Committee hearing Wednesday that he would place a hold on R. Clarke Cooper’s nomination to be an assistant secretary of State amid a fight over the guns.

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“Until the president agrees to reverse this policy and prohibit the online publication of these dangerous blueprints — a decision that is entirely within his authority — I intend to place a hold on your nomination,” Markey said.

He added that while Cooper, who would oversee the State Department’s bureau of political-military affairs, wasn’t responsible for the administration’s policy, “You are asking us to confirm you to a position where you will be defending the indefensible.”

Placing a hold on Cooper’s nomination can’t prevent him from being confirmed, but it would force Senate Majority Leader Mitch McConnell (R-Ky.) to use up days of floor time to get him confirmed once his nomination is brought to the floor.

A federal judge issued a temporary restraining order on Tuesday blocking the online release of plans for 3D printed guns, hours before the blueprints were set to become available.

The administration has come under criticism for a legal settlement with a gun rights activist last month over the distribution of 3D firearm blueprints. Defense Distributed sued the U.S. government in 2015 after the State Department forced all of its instruction manuals to be removed from the internet.

Under the terms of the court settlement, Defense Distributed was expected to be allowed to start publishing digital blueprints on its website starting Aug. 1. But thousands have already been downloaded when some plans were put online early.

Democrats on Tuesday introduced legislation that would ban blueprints of 3D printed guns from being posted online. Sen. Bill Nelson (D-Fla.) tried to pass the legislation by unanimous consent, but Sen. Mike Lee (R-Utah) objected, saying he had First Amendment concerns.