The tax bill is a penalty for not making proper estimated tax payments. If you owe $1000 or more in state and county tax not covered by withholding taxes, or, if not enough tax was withheld, you can make estimated tax payments. If you did make estimated tax payments, they were either not paid on time or you did not pay enough to cover the tax owed.
Learn more in Information Bulletin #3 or by contacting DOR.