A commission is the amount of money a person earns when he/she sells something. The law says that commissions are in fact wages that an employer must pay. If an employer pays an employee on a commission pay arrangement, then it must pay him/her when the commission is earned. The employment agreement sets forth when this takes place. An agreement, for example, may say that a commission is earned when a customer signs a sales agreement to buy a good or service. Despite the "earned" requirement on this method of payment, most of these pay arrangements operate on a semi-monthly basis. This means the worker will receive two paychecks a month on set days.