Groups opposed to public access to Rocky Flats National Wildlife Refuge, where for decades workers made components for nuclear weapons, will file a motion for a preliminary injunction in federal court Wednesday to block construction of a visitor center or trails.

The group said in a press release Tuesday that work at the 6,200-acre refuge “is likely to begin soon if the U.S. District Court does not intervene quickly.”

The request for a preliminary injunction comes just two weeks after the plaintiffs, including Rocky Mountain Peace & Justice Center, Candelas Glows and Rocky Flats Right to Know, sued federal officials over an anticipated summer 2018 opening of the refuge. They claim the environmental risks of allowing the public onto the site, where workers processed and stored a vast mix of toxic chemical and nuclear substances, have not been adequately analyzed.

Clean-up of the site, which sits less than 20 miles northwest of Denver, was completed a dozen years ago at the cost of $7 billion. It was established as a national wildlife refuge in in 2007.

U.S. Fish and Wildlife Service refuge manager David Lucas told The Denver Post earlier this month that the visitor center hasn’t been fully designed, and construction wasn’t planned to start any time soon.

It’s not clear why the plaintiffs feel construction is imminent. A copy of their motion wasn’t available Tuesday.

A press conference by those opposed to the refuge’s public opening is scheduled for 11 a.m. Wednesday at the Alfred Arraj U.S. District Courthouse in Denver.