U.S. Sen. Catherine Cortez Masto said she plans to slow all nominations to the Department of Energy until the agency agrees not to send any more plutonium to Nevada and provides a date for when the secret plutonium shipment will be removed from the state.

“I’ve said before that I will be shining a bright light on the Department of Energy’s secret shipment of weapons-grade plutonium to Nevada,” Cortez Masto said in a statement provided to The Nevada Independent. “Until I’ve gotten commitment from [Energy] Secretary [Rick] Perry that his agency will stop any further shipment and set a date for the removal of the plutonium already in the state, I will be putting a hold on all DOE nominees.”

Cortez Masto’s move, which is called a “hold” in Senate parlance, will require Senate Republican leaders to take roll call votes on any DOE nominees in order for them to be confirmed, which takes up precious time on the Senate floor and slows the advance of other GOP priorities.

A simple majority vote is all that it takes to cut off debate and confirm such nominees since 2013, when former Senate Majority Leader Harry Reid of Nevada used a procedural maneuver to lower the threshold for overcoming a filibuster. Prior to 2013, confirming executive-branch nominees required 60 votes. With Republicans controlling 53 of the 100 votes in the Senate, a simple majority is easily achieved, though going through the process is time-consuming.

The Senate can move nominations quickly under what is known as “unanimous consent,” in which all senators agree to allow a nominee or bill to advance, shortening the time the Senate spends on the matter. The procedure has historically been used for non-controversial nominations or issues.

Four DOE nominees were advanced last week by the Senate Energy and Natural Resources Committee, of which Cortez Masto is a member. She voted against all of them in committee.

The four nominees are Rita Baranwal, picked to be assistant secretary for nuclear energy; William Cooper, chosen to be general counsel;  Christopher Fall selected to be director of the Office of Science; and Lane Genatowski, picked to be director of the Advanced Research Projects Agency.

The DOE in January admitted that it had already delivered a shipment of a half ton of weapons-grade plutonium before Nevada took the DOE to court in November. The admission came as a result of a lawsuit filed by the state to prevent any shipment of plutonium.

Gov. Steve Sisolak and the Nevada congressional delegation have said they were shocked because the state had been in talks with the DOE before the lawsuit was filed to prevent any such shipment. The DOE maintains that the disclosure should not have been a surprise since the agency told the state the shipment was possible and that the agency  was working on a plan, which sparked the negotiations prior to the lawsuit.

The plan to temporarily store plutonium in Nevada is the result of the DOE’s failure to meet a deadline to complete construction on a South Carolina facility that is meant to repurpose excess plutonium into fuel for nuclear reactors. A federal judge in May ordered that one metric ton of plutonium be removed from the site.

The DOE has said it does not plan to ship the other half ton to Nevada, but Sisolak and the delegation want something more binding because, they argue, the DOE acted in bad faith by not disclosing anything about the shipment until January in the court filing, despite being in talks with the state on the matter before Nevada’s lawsuit.

Sisolak has requested a meeting with President Donald Trump on the matter and on building a nuclear repository at Yucca Mountain. The White House has indicated that it is open to working with the state, but no date has been set.