The following links describe the ethical considerations and hazards encountered when therapists are asked by a client (or a client's lawyer) for a letter of support or similar statement.
"Sometimes it's What You Don't Say . . . ."
Michael Griffin, JD, LCSW, Staff Attorney, California Association of Marriage andFamilky Therapists, March/April 2013. [PDF]
Strategies for Private Practitioners Coping With Subpoenas or Compelled Testimony for Client Records or Test Data.
Committee on Legal Issues American Psychological Association, Professional Psychology: Research and Practice, 2006, Vol. 37, No. 2, 215–222, Copyright 2006 by the American Psychological Association
Book link: Ethics in Psychotherapy and Counseling: A Practical Guide (5th Ed.)
by Kenneth S. Pope and Melba J. T. Vasquez