April 2 (Reuters) - Pharmaceutical company Akorn Inc. said it received a warning letter from U.S. regulators citing significant deviations from good manufacturing practices at its Decatur, Illinois plant. The company said the warning from the U.S. Food and Drug Administration will affect the manufacture of IC-Green, its intravenous dye, and hurt first-half 2007 revenue by about $2 million. Akorn said it will immediately seek a contract manufacturer for IC-Green. The Buffalo Grove, Illinois-based company said the FDA may also withhold approval of pending new drug applications that list the Decatur plant as a manufacturer until the violations are corrected.