The city of Denver has frozen the bidding process for the quarter-billion-dollar expansion of the Colorado Convention Center after discovering misconduct, according to a news release issued Tuesday afternoon.

Earlier this year, companies submitted competitive bids to design and build the $233 million project. The city was preparing to interview bidders when the City Attorney’s Office discovered the process was “irreparably compromised by non-city participants,” the city announced in the news release.

The city has asked the Denver District Attorney’s Office to investigate. The DA’s office is reviewing the material but hasn’t made any decisions about its next steps.

The city alleges that the process was compromised by the “improper release of city documents to a contractor bidding on the project; improper discussions about the bidding process; and altering of approved project plans.”

Denver officials haven’t detailed who committed those alleged actions, but the news release said the city will terminate its $9 million contract with Trammell Crow for program management services. It also said Public Works Director Eulois Cleckley is “requesting a review of Mortenson’s prequalification status for bidding on future projects.”

Mortenson was one of three bidding companies to make the project’s shortlist.

“We believe this is a significant breach of the public trust and a willful violation of a competitive bidding process,” Mayor Michael Hancock said in the news release. “We will never tolerate this type of behavior from our contractors and will continue to address this swiftly and aggressively.”

Bill Mosher, senior managing director of Dallas-based Trammell Crow, responded Tuesday: “The alleged actions in connection with the Colorado Convention Center project have in no way been authorized by Trammell Crow Company and are contrary to the firm’s values and longstanding business practices. We are cooperating fully with the City and are conducting our own internal investigation.”

The company is a prominent player in Denver development. It had a major role in the Union Station redevelopment project and it is the master developer of Denver Water’s $196 million redevelopment project.

Mortenson also is conducting an internal review of its participation in the bidding process and will cooperate with the city’s and DA’s investigations, said Maja Rosenquist, the contractor’s senior vice president.

“We’ve received a letter from the city and county of Denver concerning termination of the RFP for the Colorado Convention Center Expansion project,” Rosenquist said. “We take the issues raised by the city very seriously and are committed to addressing this matter thoroughly and appropriately.”

In addition to Mortenson, Hensel Phelps Construction Co. and PCL Construction Services also made the shortlist to compete for the project, according to public works spokeswoman Nancy Kuhn. The city mentioned neither of those companies in its news release.

Voters approved partial funding for the convention center expansion in 2015.

If you have relevant information, email akenney@denverpost.com or call 303-954-1785.