If you call in sick to work and the person has to hire someone from a temporary agency.

It is not clear what all of the relevant facts are. As a general matter, if you do not work, you do not get paid. This is true for hourly employees and even for salaried employees if the absence is a full day. So, if you are paid on a salaried basis, your employer can deduct the portion of your salary that relates to the day of your absence. Unless you have agreed to such an arrangement in advance, your employer probably cannot deduct anything beyond the ratable portion of your pay related to the period of absence.