NEW YORK (CNNMoney.com) -- Aircraft maker and defense contractor Boeing could be liable for further payments due to an ongoing Air Force review of a tainted cargo-plane contract stretching back to 2000, according to a published report.

A Boeing spokesman told the Wall Street Journal that, depending on the review, the entire $412 million it received in a November 2000 contract adjustment could be subject to renegotiation. Discussions over the matter, should they occur, are likely to stretch on for months, according to the report, which added that the extent of Boeing's liability isn't clear.

Boeing's C-17 cargo jet. A report says the Air Force is still probing a $412 million payment Boeing received for the jet in 2000, despite the company's June settlement with the Justice Department.

Boeing already agreed in June to pay $615 million to the Justice Department to settle a series of criminal and civil investigations related to its defense contracts. The company is the No. 2 supplier to the Pentagon.

Former Air Force acquisition chief Darleen Druyun went to prison for conducting improper employment talks with Boeing while she negotiated the C-17 contract adjustment. When the $615 settlement was announced, the Justice Department's statement said Boeing was released from "any civil liability arising from the Druyun matter."

But the Journal reported that a letter Boeing wrote to the Air Force the same day said that lingering questions about the propriety of the C-17 payment negotiated by Druyun weren't resolved by the broader agreement.

Boeing lawyer Paul Ehlenbach wrote that the Air Force deputy general counsel in charge of acquisitions the company "would agree to reopen" that matter and "engage in good faith negotiations" to reach a compromise if the Air Force review determines the $412 million payment was not "fair and reasonable," according to the report.

Shares of Dow component Boeing (Charts) were down 2 percent in early Frankfurt trading on the report, as well as on the news that British authorities had arrested 21 people accused of a terrorist plot to blow up commercial flights over the Atlantic.

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