It depends on the agreement between you and your employer, if any, or else on the employer's policy for paying commissions. Unless the employer has an explicit policy on this, you've got a pretty strong position.
You would have to look at your employment contract. Salary / hourly wages cannot be deducted from, but if your commission can be zero if the loss on won order cancels the profit from another order.
You should contact an attorney in your area to review your employment contract and discuss all the facts.