Updated 4:05 p.m., with comment from Yahoo.
A Department of Justice probe into hiring practices among high-tech firms appears to have stretched out to include some of the best-known names in the industry.
The Washington Post first reported the story on Tuesday evening, listing Apple, Yahoo, Google, and Genentech as among the companies that were being looked at. Microsoft and Intel are also believed to have received requests for information, according to sources as well as to a New York Times report.
The issue is believed to center on whether certain companies agreed not to hire from one another.
Microsoft, Apple, Google, and Intel all declined comment. Late on Wednesday, Yahoo confirmed it had received an inquiry from the government "a while ago."
"We have been contacted (by the DOJ), and we are cooperating," a Yahoo representative said.
Word of the probe took some in the tech industry by surprise, given several prominent cases of tech firms suing one another over worker poaching. Two of the companies said to be involved in the probe--Microsoft and Google--waged a fierce, multistate court battle after Microsoft executive Kai-Fu Lee was hired by Google. (The two sides eventually settled.)
More recently, Apple and IBM duked it out after Apple hired IBM executive Mark Papermaster. He eventually took up work at Apple, but only after a lawsuit and eventual settlement. IBM also sued over a recent Dell hire, David Johnson.
CNET News' Tom Krazit contributed to this report.