John Mackey's postings on Yahoo Inc. (NASDAQ:YHOO) stock forums from 1999 to 2006 lauded Whole Foods and disparaged Wild Oats Markets Inc., a Boulder, Colo., natural foods chain Whole Foods made a $565 million bid to acquire in February.

The U.S. Federal Trade Commission sued to block Whole Foods' purchase of Wild Oats June 6, alleging the combination would violate antitrust law by reducing competition and raising consumer prices.

A special board committee has retained legal counsel to advise it during its Mackey investigation, Whole Foods said. The board said it would not comment further until the investigation is completed.

Mackey apologized and expressed remorse for his postings, made using the pseudonym Rahodeb, a rendering of Deborah, his wife.

"I am very sorry and I ask our stakeholders to please forgive me," he said.

The 196-store Austin grocer also confirmed the U.S. Securities and Exchange Commission contacted it Monday about an SEC staff investigation of the postings. Whole Foods will fully cooperate with the probe, it said.