As the Keeper of the Payroll I get to process child support garnishments on our employees all of the time. Basically, some parents enter into an agreement with the state...say take $200 from each paycheck, no matter how much I make. We like those, easy to compute.
Then there are the ones that are a percentage of the their net pay. If they are supporting a "new" family then they can only take 50% of the after taxes pay, if they don't have another family they are supporting then the state can take 60%. Plus they can take an extra 10-15% if they are behind on their child support. Pain in the butt to compute!
That being said, most of the people that are on the percentage basis will quit their job as soon as the garnishment starts. They just simply can't live on the 40-50% of their paycheck that is left. So what I like to do is call the employee being garnished and convince them to call the state and try to work with them, normally they can call the state and say "hey I only bring home $200 a week, here are my bills, rent, etc... can I have a more reasonable amount ganished. The state usually will say, ok, you make $200 per week, let's have your employer take $50 per week out for child support instead of $100.
I've had a lot of employees call me and thank me for telling me to do that. Odds are they just go from job to job, running away from the garnishment, because even though we report them to the state, it takes a couple of months for them to prepare and send the garnishment to the employers. I figure it is better for the parents to finally stop running and better for the kids because then they are getting a steady amount of support.

The state does review their wages periodically and will make an adjustment up or down if their pay changes.
Now some of the states allow a person to make a certain amount before they start garnishing. For example, Oregon says they can take home about $180 per week before they start garnishing. It is normally tied to the federal minimum wage.
Hold it, weren't you the lady telling me how easy this camping trip was going to be a few days ago!