Bain Capital, Blackstone Group and Texas Pacific Group met with New York Stock Exchange Chairman John Thain in June to propose that the three private-equity firms take out a stake in NYSE, the Big Board reveals in a regulatory filing in connection with its planned merger with Archipelago Holdings Inc.

The investor group proposed providing capital to the NYSE in exchange for some or all of the NYSE memberships, Dow Jones reports. Thain told the firms that the NYSE wasn't for sale, that it "did not need any private equity and that it was unlikely that an acquisition of all of the equity of the NYSE by one or a few private equity firms would be approved by regulators," according to the NYSE filing.

Thain later told the exchange's board about the approach. Since then, not one of the companies has proposed any transaction, the filing said. Meanwhile, NYSE maintains the Archipelago merger will help it expand its business and has already produced an increase in the value of its membership seats.

But not all NYSE members are happy with the deal. One group has filed a lawsuit to block the deal, which the NYSE is fighting.

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