Now that the U.S. Justice Department has put the kibosh on price-fixing as a way to hold the line against new digital competitors, the next obvious step for old-line publishing houses trying to weather the inevitable transition from hard-copy to digital is consolidation. Last month, Penguin and Random House announced plans to merge, reducing the number of major publishing houses from six to five.  Now comes word via the Wall Street Journal that News Corp.’s HarperCollins unit has approached CBS about acquiring Simon & Schuster.

The feds could still end up having a major say in the matter, however. Any proposed mergers among the major houses will have to through a thorough antitrust review, by either the Justice Department or the FTC, before being allowed to go forward. And with regulators already on alert for anti-competitive behavior in the industry, getting the green light is far from certain.

Random House was the only one of the Big Six not charged in the Justice Department’s ebook price-fixing conspiracy case against Apple and the major houses. Penguin was among those charged, as were HarperCollins and Simon & Schuster.

Unlike the latter two, however, Penguin has so far declined to settle with the feds. It’s now clear that talks with Random House were already underway in September, when the settlement by the other publishers was approved by the court. It’s possible Penguin decided that acknowledging behavior the government regarded as anti-competitive (even without admitting legal wrongdoing) would hurt it in the inevitable antitrust review of its planned merger.

Whether that turns out to have been the right call could now depend on how the government responds to any proposed merger between HarperCollins and S&S, both of which have tacitly acknowledged engaging in price-fixing and collusion, if only by agreeing to stop doing it.

This story has a long way to go still, and the ending is yet to be written.