When a divorce or juvenile court is considering setting a support amount, the court must try to determine the actual income of each parent.
In some cases, one of the parents is either unemployed or has a job where they are really making much less money than there experience or skills would otherwise dictate (otherwise referred to as "under-employment").
In these situations, the court can take evidence as to whether that parent is "voluntarily" unemployed or under-employed. The Court can hear evidence about that parent's past employment, why that past employment was terminated (or modified as to salary or wages), and can also have "vocational" experts testify as to the real employment possibilities of that parent.
Every so often one party in a support proceeding will actually quit their current job or deliberately pursue a lower paying opportunity - just so they can argue a lower ability to pay support. However, with the right evidence, this tactic can be rebutted.
Most divorce and juvenile courts are very experienced with this issue, so a party to one of these support actions should be aware that unemployment and under-employment tactics are sometimes very easy to spot.