Atmel ( ATML) shares plunged Tuesday after the San Jose, Calif., chipmaker delayed its second-quarter earnings report, becoming the latest company embroiled in a growing controversy surrounding stock-option practices. The company said Tuesday that it has begun an internal investigation regarding the timing of past stock-option grants and other related issues. The investigation is being led by the board of directors' audit committee, with assistance from independent legal counsel and accounting consultants. Atmel said it would not be able to file its report for the three months ended June 30 until after the investigation is completed. As a result, Atmel will not release its second-quarter earnings report or hold a conference call to discuss the results that was scheduled to take place Tuesday. Shares of Atmel recently lost more than 14%, shedding 69 cents, to $4.13. Atmel noted that it does not expect the investigation to be completed by the Aug. 9 due date for its 10-Q report or by the Aug. 14 extension. Several semiconductor companies, including Altera ( ALTR) and Applied Micro Circuits ( AMCC), have received notices from Nasdaq threatening to delist their stocks because of missed deadlines stemming from backdating investigations. Atmel did not indicate whether it expected to receive such a notice and stated that its executives will refrain from commenting further until the investigation is completed.