You should hire a lawyer if you want to prove intentional underemployment. It is very fact-specific and will require presentation of witnesses and evidence. You don't have time to master those skills by the trial. Also, there are very tight pleading rules so you need a lawyer to draft your petition.
This answer DOES NOT establish an attorney-client relationship. This answer is based on the limited information provided and is not intended to be conclusive advice. There are likely other factors that might influence or change the advice after a more lengthy consultation.
I agree with Ms. Lowry that you will need an attorney to help you accomplish what you want. Additionally, the outcome will depend heavily on the specific facts that can be proven as well as who the judge is, but one possibility of being found in contempt is being put in jail. It happens all the time to parents who fail to pay court ordered child support.
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