Mortgage underwriters normally want documentation attached to the letter of explanation. For example, a letter of explanation may be required if a mortgage loan borrower had a substantial low income one year from the previous year and had a late payment history for three months.
Wage garnishment by itself will not damage your credit...and the fact that your wages are being garnishment will not be noted on your credit report....However, the judgment that led to the garnishment (if they report it) will affect your credit rating...and the original default of your credit card will also still damage your credit rating.
Deductions not required by law are not subtracted from gross earnings when the amount of disposable earnings for garnishment purposes is calculated. Wage garnishment occurs when an employer withholds the earnings of an individual for the payment of a debt as the result of a court order or other equitable procedure. You can't be fired from your job for one garnishment, but federal law doesn't protect you if you have multiple garnishments.