自己要求吧，读一下这个文章。

http://www.lexology.com/library/detail.aspx?g=877f4b0d-913c-4dbe-9283-358ade93e773

On the issue of paying fact witnesses, the court stated that it is not improper to pay a fact witness at his or her professional rate for lost time. The court noted that federal courts generally hold that a fact witness may be reimbursed for expenses incurred and compensation lost because of the litigation. Further, the court acknowledged that American Bar Association Ethics Opinion No. 96-402 states that it is proper for parties to pay fact witnesses for their loss of hourly wages or professional fees. Thus, the court of appeals concluded that it is not improper to pay fact witnesses in the State of Tennessee.