Cain himself acknowledges this:
BTW, I am in favor of the 9-9-9 plan because it will dramatically change incentives in favor of job creation and savings and broadens the base to ensure that more Americans have skin in the game.
If the cost of labor is not allowed to be deducted it will make it impossible for a labor intensive business to start up as they may be operating at a loss for at least a year or two and will still be required to pay 9% on their gross. Even when they start to make a profit the 9% could possibly amount to much more than the current 35%. It all depends on what % labor is of their total costs.