Your letter of recommendation should come from a faculty member who knows your academic and/or research work.
The Family Educational Rights and Privacy Act (FERPA), enrolled students have the right to view the contents of their university records. If a recommendation is part of a student's record, he/she is entitled to see it. Waiving this right means giving up the right to see the recommendation. Deciding whether or not to exercise this option is difficult, because it is impossible to know how an individual receiving a request for a recommendation will react to a student's decision to retain his/her "right to know."