Your tax return is complete but instead of a refund, you get hit with a huge tax bill. Do not fret. Outside of a few narrow circumstances, the IRS cannot levy your income or assets without first providing you with proper notice. By law, the IRS must give the taxpayer notice and demand for payment also known as a CP 501 notice. This essentially means that you have a balance due to the IRS. The IRS must also provide the taxpayer with a notice of intent to levy and notice of your right to a hearing. This notice is usually issued once the IRS has notified you of a balance due and the account remains unsatisfied. This notice also allows you to preserve your appeals rights.
If you are unable to pay your tax balance in full, do not simply ignore the notices that come in the mail. Instead, you (or your tax professional) can contact the IRS to discuss alternative resolutions. One resolution is an installment agreement, which allows you to pay down your liablity in manageable monthly payments. Alternatively, you can request an "Offer in Compromise" whereby the IRS may settle the liabilities for less than the full amount of what is owed. Like the installment agreement, this repayment option is contingent upon your current financial situation and convincing the IRS that it is in its best interest. A third option is currently-not-collectible status which keeps the IRS from pursuing any forced collection against you as long as you remain current with all of your personal tax obligations. The option is only available for those who due to insufficiency of income are unable to pay their taxes.
Of course the best resolution would be to full pay your liability, but if you are unable to do so, please know that you have options. If you are unsure of these options or do not feel comfortable negotiating with the IRS on your own, you should contact a tax professional.