A debt collector can negotiate what he or she desires the monthly installment amounts be on an outstanding obligation and request that income information be shown to assist in arriving at an agreed upon monthly payment amount. However, the information cannot be forced to be given by you.The threatening of bank and income garnishment as part of the negotiation process could very well be an unfair debt collection practice under your state's and federal law, "Unfair Debt Collection Practices Act."Other comments or "threats" by the debt collector as to attempts to obtain income information from you likewise could be an unfair debt collection practice,You should consult with an attorney on the subject. If you cannot afford one, call your local county bar association. It may have a program where attorneys conduct free clinics to assist people like you needing help.Good luck.