No, if you are going on a sales call, you are working: while it is legal to pay you for that time commission only (subject to you overally being paid at least minimum wage for the week, based on the number of hours total you worked), you may not be made to use a vacation day for performing work or work travel. That said, if the employer will not see reason and makes you use a vacation day, the only way to get compensation for it would be to sue your employer and win. Lawsuits cost money (though not much if you represent yourself "pro se", take time, and will obviously affect the relationship between you and your employer; the employer may terminate you for suing it, for example). Therefore, it be difficult or impossible to vindicate your rights while employed. You may wish to seek other employment, then after you have a new job, look into suing to recover the value of the vacation days you were forced to improperly use.