There are limits on what can be withheld. Based on the arrearage and whether you have other children in your home that you are legally required to support, the percentage can be as high as 65%. This assumes no other children to support in your home and more than 12 weeks in arrears. If you have other children to support in your home then the max is 50%. Even then they can take an extra 5% if the arrears are more than 12 weeks worth of support.