It isn't just new investors whom private equity giant Blackstone will have to sell on its upcoming IPO. Both before and after the firm made the showstopping March 22 announcement that it would sell 10 to 15 percent of its core partnership to the public, it reached out to its skeptical limited partners, largely pension funds.

In phone calls and e-mails, general partners of the New York­based powerhouse stressed that Blackstone wouldn't give up an iota of control to public shareholders. Instead, the firm is setting up a "master limited partnership," which will function much like the dual-class shareholder structure in place at such firms as New York Times Co. and Google. Public shareholders will be disenfranchised investors, sharing only in economic benefits -- and these could be constrained because maximizing returns for limited partners will continue to be Blackstone's "guiding principle," according to its prospectus.

Not all limited partners are sold -- especially those with large stakes in Blackstone funds.

"Generally, when a private equity, hedge fund or traditional asset manager goes public, it's not good for limited partners," says Stephen Nesbitt, CEO of Cliffwater, an investment consulting firm in Marina del Rey, California, who advised many of the limited partners on the deal. "It comes down to 'How bad is it?'"

Some of the limited partners worry that the interests of the new class of public shareholders are likely to diverge from their own. Public investors may have shorter investment horizons; they may also be less inclined to reinvest returns and less likely to be tax-exempt.

"Going public is like having a baby," says Larry Ribstein, a professor at the University of Illinois College of Law, in Champaign. "You might tell your spouse nothing will change, but that can't be the case when the baby comes." He notes that public shareholders will invest as much as $4 billion in Blackstone. Even though the firm says its offering limits its fiduciary duties to public shareholders, Blackstone hasn't disclaimed all such duties and still has an obligation of good faith, Ribstein adds.

Blackstone's limited partners fear that a new class of public stockholders might circumscribe the firm's ability to share information. Typically, the firm keeps limited partners updated on current valuations of portfolio companies. An even greater degree of information is often revealed when Blackstone reaches out to limited partners for co-investment capital that is funneled into individual portfolio companies. But the firm, whose ability to operate under a shroud has been key to its strategy, will now have to weigh the impact and legality of how it disseminates information.

"Both Blackstone and the shareholders need to take appropriate measures that information isn't being leaked to those who might be in a position to trade on it," says Robert Kennedy, a partner at law firm Jones Day in New York who has worked on private equity deals.

Fees may also become more contentious: Large limited partners often tussle with general partners to reduce management fees. But public shareholders, who will profit from those payments, will be aligned with general partners.

Blackstone, of course, downplays these concerns. In a memo to the limited partners, CEO Stephen Schwarzman and senior managing director Kenneth Whitney said that the infusion of new capital would allow for "further aligning our interests with those of our Limited Partners." Attorneys also say that given the size of the firm, and the relatively small share that will be held by the public, its ability to share information would be unaffected because messages would not likely be material.

"We'll never be completely assuaged by their arguments," says one limited partner. But given Blackstone's performance -- an annualized net return of 22.8 percent since 1987 in its corporate private equity funds -- limited partners remain buyers in a seller's market.