The law is in the Code but it is not something that is stated in a straight forward manner. The below will explain why a Treasurer’s Lien for taxes can reach 100% of an employees pay. The Treasurers’ Lien is not subject to the general garnishment limitations, which includes a cap at 25% of disposable earnings. These liens are also not limited by the federal garnishment limitation (excluding 40 times the minimum wage from the reach of creditors). The reason tax liens are not so limited is because they are expressly excluded in Code of Virginia §34-3.

§ 34-3. Articles not exempt from taxes or levies or for their purchase price.
The exemptions under §§ 34-4, 34-4.1, 34-26, 34-27, 34-29, and 64.1-151.3 shall not extend to distress or lien for state or local taxes or levies, nor to levy, distress, or lien for the purchase price of any articles claimed as exempt or any part of the price thereof nor for fines and damages or either arising from trespass by animals under § 55-306 as to such animal so trespassing. If an article purchased and not paid for is exchanged or converted into other property of the debtor, such property shall not be exempt from payment of the unpaid purchase money debt.

Code of Virginia §34-29 referenced here imposes the 25% limitation and it expressly does not apply to liens for local taxes.The Federal limitations also do not apply to the collection of local taxes pursuant to the Code of Federal Regulations. ( 5 C.F.R. 582.402(b))