(a) Any order of support of a child entered or modified on or after July 1, 1985, shall contain the following provision:

"Whenever, in violation of the terms of this order there shall have been a failure to make the support payments due hereunder so that the amount unpaid is equal to or greater than the amount payable for one month, the payments required to be made may be collected by the process of continuing garnishment for support."

(b) Any order of support entered or modified prior to July 1, 1985, shall be construed as a matter of law to contain the provision set forth in subsection (a) of this Code section.

(c) All Title IV-D (child support recovery) cases involving orders of support of a child or spouse entered or modified prior to July 1, 1989, or thereafter shall be subject to income deduction as defined in Code Sections 19-6-31, 19-6-32, and 19-6-33.