jamie jones left a voice mail asking you to withhold an additional $40 of federal income tax from her wages each pay period, starting june 1. when should you begin withholding the extra amount?

Begin withholding the additional 40 dollars on the first pay period on or after June 1. In other words, you do not wait for any special confirmation; you start with the first paycheck whose pay period begins on or after June 1 and include the extra 40 dollars of federal income tax from that point forward.