Chicago-based General Growth Properties Inc. may be prejudiced in favor of a risky bid from Brookfield Asset Management Inc. because of that company’s agreement with William Ackman’s Pershing Square Capital Management LP, creditors said in court documents.

The bankrupt owner of more than 200 U.S. malls from Boston to Los Angeles, which also had an unsolicited $10 billion offer from Indianapolis-based Simon Property Group Inc., shouldn’t be allowed to control its bankruptcy for six more months, unsecured creditors said in papers filed Tuesday in U.S. Bankruptcy Court in Manhattan.

Creditors added reasons to their prior objection, citing a Feb. 24 agreement between Pershing and Brookfield and a “risky” buyout plan. Simon also filed a new objection Tuesday, citing that deal. Under General Growth’s plan, Brookfield would be the so-called stalking horse bidder to compete with other potential buyers.

The agreement puts General Growth, whose board members include Ackman, “into an obvious conflict of interest situation where the debtors must choose between the best interests of the estate and the economic interests of one of their most active and vocal directors,” lawyers for unsecured creditors wrote.

“Ackman, therefore, now has a unique and personal interest in making sure that Brookfield is approved as General Growth’s stalking horse,” lawyers for Simon wrote.

General Growth, in support of its bid to keep control over its bankruptcy, has said it’s pursuing a “dual track” process that will consider both mergers and financial bids. It said in court filings Monday that it will seek competing bids to Brookfield’s and that it aims to confirm a reorganization plan by Oct. 5.

U.S. Bankruptcy Judge Allan Gropper, at a hearing Wednesday, is scheduled to consider General Growth’s request for an extension of its exclusive right to file a reorganization plan.

Ackman is a founder and principal of Pershing, which owns 25 percent of General Growth’s stock, according to creditors. Under the “interim bid protections” agreement, Pershing will pay 25 percent of its profits above $12.75 a share to Brookfield if other protections for Brookfield aren’t approved by the bankruptcy court and if the company reorganizes with an investor other than Brookfield, creditors said.

The accord also gives Toronto-based Brookfield warrants to buy 60 million General Growth shares at a strike price of $15 each over seven years, after the earlier agreement expires, creditors said.

General Growth said it plans to seek approval April 13 of a formal bid-protection agreement to aid Brookfield as a stalking-horse bidder. Such agreements, designed to compensate a company for time and money spent evaluating a potential acquisition, are standard in bankruptcy auctions.

General Growth said in a Feb. 24 statement that it would offer the warrants and interim protection as compensation for Brookfield’s financial commitment to its offer.

Creditors said the Brookfield proposal is risky for them because it depends on more than $5.8 billion in debt and equity raises and asset sales in addition to Brookfield’s investment. The proposal might convert their debt to stock in a new company that is at “an artificially high valuation” creditors said.