Kohlberg Kravis Roberts, the Carlyle Group and Silver Lake Partners are among the firms that have received letters from the Justice Department seeking broad information about business practices going back to 2003. This seems to be the start of a wide-ranging probe about private equity firms, which have increasingly been joining forces to make bids. Does joint action limit competition and keep prices low? Not always: Note the battle for Freescale Semiconductor, which pitted a KKR Group against The Blackstone Group and raised the bid. The Blackstone Group did not receive a letter. Still, there are lots of cozy relationships among firms these days. You have to wonder what kind of side deals are cut. Responding to the letters is voluntary.

For more on the probe:
- Here's a New York Times article