Tables for figuring the amount exempt from an IRS levy (like garnishment) on wages, salary and other income are located in Publication 1494 at www.irs.gov. Simply put, the amount of money exempt from the levy, i.e. the amount you get to take home from your paycheck, is determined by your filing status (single, head of household, married filing jointly or separately) and the number of exemptions (dependents, e.g.) you can claim.
When your employer recieves a notice of the levy, your human resources person will give you a form to fill out. There you will mark your exemptions and filing status. From there, the tables in Publication 1494 take over. For example, a single taxpayer paid weekly with 3 exemptions (including one for the taxpayer) has $325.00 exempt from the levy. In other words, not much.
The wage levy will remain in place until the debt is extinguished, or you work out payment arrangements with the IRS, or you quit your job. See our other FAQ's for what to do when a wage levy occurs.