Illegal wage garnishment - what to do?

You didn't mention the reason why you think the garnishment is illegal. Is there any judgment against you?
If you want to stop the garnishment, act quickly. You might have 5 to 30 business days before the garnishment starts.
Check out the instructions written on the garnishment document you receive from the court.

Normally, you'll find the form attached with the garnishment notice. If it is not, you may ask the court to send the notice again along with the form. You may also write an objection letter yourself and file it timely.

If it is illegal, you can get the money back. I will suggest you seek a lawyer's help.

Usually the creditor/CA has to win a judgment from the court to inform an employer to garnish wages.