For-profit education provider Apollo Group Inc said the U.S. securities regulator was probing certain share sales by company insiders.
The Securities and Exchange Commission contacted Apollo seeking information about the stock sales and a regulatory filing on February 28 that disclosed the company's second-quarter outlook, Apollo said in a regulatory filing on Thursday.
On February 28, Apollo said it expected to sign up fewer new students in the second quarter, sending its shares down as much as 16 percent.
Apollo did not reveal the name of the insiders involved.
BMO Capital Markets analyst Jeff Silber said while the SEC probe adds another element of risk to the stock, the company has relatively robust insider trading controls given the heightened scrutiny under which it operates.
For-profit colleges, including Apollo's University of Phoenix, have faced scrutiny from the U.S. government over the last two years after findings of high student debt load, low graduation rates and fraudulent activities.
Apollo said it intends to fully and voluntarily cooperate with the SEC's preliminary investigation.
The company's shares, which have fallen about 35 percent since the outlook warning in February, were down 2 percent at $35.20 on Thursday on the Nasdaq.