From the Department of Labor information notice regarding wage garnishment:

"Title III also protects individuals by limiting the amount of earnings that may be garnished in any workweek or pay period to the lesser of 25 percent of disposable earnings or the amount by which disposable earnings are greater than 30 times the Federal minimum hourly wage prescribed by Section 6(a) (1) of the Fair Labor Standards Act of 1938. This limit applies regardless of how many garnishment orders an employer receives. The Federal minimum wage is $7.25 per hour."

It also states that if state limits are smaller than the state limits apply.