If the IRS has put a tax lien on your company, it can be very difficult to continue doing business. You may lose control of your accounts receivable, and suddenly be unable to obtain credit. Your business might not grind to a complete halt, but a tax lien can be a serious drag on your ability to function and grow.
If the IRS accuses you of failing to pay a tax debt, the agency may try to put a tax lien on your property. A lien can cause serious trouble, because it severely restricts your ability to use or transfer your assets, such as real estate or a small business, as you see fit.