It is unconstitutional. One of the findings that a judge has to make before he puts anyone in jail for failing to pay child support is that the defendant either:
1) Has the present ability to make the payment; or,
2) Would have the present ability to make the payment but for a deliberate or reckless suppressing of his income or assetts; or,
3) He had the ability to make the payment when it was due or since it became due, but failed to make the payment.
Not the way it works. You work and do not pay child support. You have the money but hide it to avoid paying child support. That is fraud and thus you are jailed for a form of fraud. If you can prove you were and are unable to pay the child support then you are not jailed. Although this may leave you with precious little to live on.
Most people jailed have made real efforts to avoid paying child support. They could have paid but instead they paid for other things cars, boats, homes, new marriages etc. Many change their names move and make sure they get paid in cash. Some even refuse to take jobs they could get and live off a new spouces income. In all these cases these cases these people should go to jail.