If you don't pay your debts, taxes, or child support, a creditor can go to court and obtain a wage garnishment. This order forces your employer to send upto 50% of your wages to your creditors to pay your debts. People often refer to as having their wages “garnished”. (The correct legal term is a garnishee or garnishment.)
In order to garnishee your wages in Ontario, a creditor must take you to court, sue you, and obtain a Garnishment Order from the court. The only exceptions would be a Credit Union that you have given an assignment of wages to, or Canada Customs and Revenue Agency (Revenue Canada can garnishee your wages without a court order).
If a creditor has gone to the trouble of garnisheeing your wages, they are not likely to stop the garnishment because you agree to pay - they only garnishee people with a history of not paying, or whom they believe will not pay.