Boeing said Thursday that it would not bid on what could be an $85 billion contract to build new nuclear-tipped intercontinental ballistic missiles, saying that the U.S. Air Force’s parameters favor Northrop Grumman, the only other company competing.

The project is considered a top priority for the Pentagon, which says it needs new-technology ICBMs to counter Russia’s own nuclear advances. The project, dubbed Ground Based Strategic Deterrent, would replace hundreds of Cold War-era Boeing Minuteman IIIs in concrete silos under the countrysides of Montana, Wyoming, and North Dakota.

“After numerous attempts to resolve concerns within the procurement process, Boeing has informed the Air Force that it will not bid Ground Based Strategic Deterrent (GBSD) Engineering and Manufacturing Development (EMD) under the current acquisition approach,” Todd Blecher, a company spokesman, said in an emailed statement. “We’ve evaluated these issues extensively, and determined that the current acquisition approach does not provide a level playing field for fair competition.”

Boeing’s decision not to bid was first reported by InsideDefense. A spokeswoman for Will Roper, the head of Air Force acquisition, was not immediately available for comment.

In a July 23 letter to Roper, Leanne Caret, CEO of Boeing Defense Space and Security, said the company feels Northrop has an advantage because it purchased Orbital ATK, a company that builds solid rocket motors originally a Boeing supplier.

Northrop initially refused to enter an agreement that would firewall Boeing proprietary data from its offices overseeing its ICBM. A Northrop spokesman was not immediately available for comment.

“Boeing has already been placed at a disadvantage in the development of its proposal by Northrop’s initial unwillingness to enter into a Proprietary Information Agreement (PIA) containing a detailed firewall plan, as the Consent Decree requires,” Caret wrote.

That agreement was finally signed on July 3, but the delay greatly reduced the work that could be done between Northrop’s rocket division and Boeing, a person familiar with the program said.

“We have been raising our concerns about the procurement at all levels of the Air Force for more than a year,” Blecher said. “But after reviewing the latest [request for proposals], it was clear that the Air Force wasn’t going to adequately address our concerns. The competition was not going to occur on a level playing field on which Boeing would have the chance to effectively compete.”

In August 2017, the U.S. Air Force awarded contracts to Boeing and Northrop Grumman to begin design and technology work on the new ICBMs. On July 16, the Air Force issued a request for bids to build about 400 of the missiles. Companies have 150 days to respond. The plan is to choose a winner by the end of fiscal 2020. Few more details are publicly available about the highly classified project.

“On the surface, Boeing’s decision not to participate in the Ground-Based Strategic Deterrent program might be viewed as a positive for Northrop Grumman, but it raises multiple questions regarding where this program is headed,” Byron Callan, an analyst with Capital Alpha Partners, wrote in a Thursday morning note to investors. “It would be unusual, in our view, for a program of this size not to be competitively bid.”

Some analysts agree that the bidding parameters favor Northrop, Callan wrote.

Rewriting those parameters could delay the program.

Boeing CEO Dennis Muilenburg made only a passing reference to the new ICBM project on the company’s second-quarter earnings call with investment analysts Wednesday: “[W]e're focused on leveraging our work to date on GBSD to help deliver this essential national security capability.”

Northrop Grumman CEO Kathy Warden was asked about the parameters on her company’s own second-quarter earnings Wednesday. “We are really seeing what we expected to see and we are positioned to be able to support the U.S. Air Force requirements,” Warden said.

“We have the knowledge and the expertise needed to put together a strong offer for the U.S. Air Force, and we look forward to doing that,” she said.

Rick Berger, a defense analyst with the American Enterprise Institute, tweeted that Boeing decision not to bid will be “Roper's toughest test of his tenure. Under no circumstances can GBSD be allowed to slip. Tough needle to thread here.”