Is a Federal Tax Lien Always Preceded by an Audit?
Unfortunately, no. Once the IRS determines that their statistical data reveals you must not have payed some tax amount, they will go ahead and seek to collect that money. If you do not pay it, and are in an appeal/audit process, they will more than likely place a federal tax lien just in case they are right. As may be expected, the best thing you can do is preserve evidence, and seek court relief later on.
