"1,000+ have already signed up to download plans to print a 3D AR-15. [Senator] Bill Nelson and I are filling emergency legislation and calling for a vote today to block this," Van Hollen said in a message posted on Twitter.
Earlier in the day, US Democratic Senator Ed Markey said in a press conference that President Donald Trump must reverse his administration's decision.
"We need Donald Trump to reverse his administration’s decision, and to do it now," Markey told reporters.
The Trump administration settled the case in June, and Defense Distributed said it would upload materials for 3D printing guns to the internet beginning on August 1.
Earlier on Tuesday, US President Donald Trump said in a Twitter message that he is looking into the issue and that he has already spoken to the National Rifle Association (NRA) about it.
In addition to the lawsuit, 21 Attorneys General wrote a letter to Attorney General Jeff Sessions and Secretary of State Mike Pompeo, asking the government to withdraw from its settlement with Defense Distributed, according to media reports.
The Second Amendment of the US Constitution guarantees the right of US citizens to keep and bear arms.