((a)) ** .—** Subject to subsection (c), if it is shown that the judgment debtor—
((1)) is receiving or will receive substantial nonexempt disposable earnings from self employment that are not subject to garnishment; or
((2)) is diverting or concealing substantial earnings from any source, or property received in lieu of earnings;
((b)) ** .—** On motion of the United States or the judgment debtor, and upon a showing that the judgment debtor’s financial circumstances have changed or that assets not previously disclosed by the judgment debtor have been discovered, the court may modify the amount of payments, alter their frequency, or require full payment.
((c)) ** .—**
((1)) An order may not be issued under subsection (a), and if so issued shall have no force or effect, against a judgment debtor with respect to whom there is in effect a writ of garnishment of earnings issued under this chapter and based on the same debt.
((2)) An order may not be issued under subsection (a) with respect to any earnings of the debtor except nonexempt disposable earnings.