Answer:
The IRS is one of the biggest collection agencies in the world. Because of it's power, it can assess garnishments on paychecks, place liens on properties, and levy bank accounts, essentially clearing them out.
It's best to set up an Installment Agreement or use other options, such as an Offer In Compromise if you have a substantial balance due.
When choosing to resolve these issues, it's best to use a Tax Resolution firm like JG Tax Group (http://www.jgtaxgroup.com), because most of the Tax Resolution Firms you see on TV are terrible - Tax Masters, Ronni Deutch and JK Harris have multiple complaints and maintain unacceptable scores with the Better Business Bureau.