At any time after the rendition of judgment the court, upon application of the judgment creditor or the judgment debtor and upon notice to the adverse party as the court shall direct, shall conduct a hearing to determine the reasonably expected annual earnings of the judgment debtor for the current calendar year and the applicable limitation upon garnishment as provided in section 642.21.  The court shall also consider in the interest of justice whether a greater amount than provided in section 642.21 shall be exempt from garnishment.  In making the determination the court shall consider the age, number and circumstances of the dependents of the debtor, existing federal poverty level guidelines, the debtor’s maintenance and support needs, the debtor’s other financial obligations and any other relevant information. An order reducing the garnishment may be modified or vacated upon the application of a party to the court, notice to the adverse party, and a showing at a hearing of changed circumstances.  An additional filing fee shall not be assessed for proceedings under this section.