Redback Networks ( RBAK) said late Friday that it received an informal request from the Securities and Exchange Commission and a subpoena from the U.S. Attorney's Office for Northern California, both of which want information about the company's past stock option awards. Shares of Redback fell 89 cents, or 4.9%, to $17.45 in premarket trading Monday. The networking company said it plans to cooperate with the matters. Additionally, Redback's audit committee has started an internal review and analysis of its historical option grants. Redback is the latest in an expanding list of companies, many of them members of the tech sector, that are voluntarily examining their past option grants or receiving requests from regulators about their programs. Redback didn't offer any specifics, but in several other cases, companies have said questions arose about whether some of their employees had options that were backdated to correspond to low share prices. Other companies among the dozens probing their option programs include Apple ( AAPL), KLA-Tencor ( KLAC) and Intuit ( INTU).