D.C. Code § 3-409
When a written complaint alleging a violation under this chapter has been filed with the Mayor, the Mayor shall initiate an investigation and, if warranted, fix a time and place for a hearing pursuant to § 2-509. The Mayor shall cause a certified copy of the charges to be served on the respondent within a reasonable time prior to the hearing. The attendance of witnesses and the production of books, papers, and documents at the hearing may be compelled by subpoena. The Mayor shall be bound by the rules of procedure and evidence in the conduct of hearings pursuant to § 2-509, and decisions shall be based upon substantial evidence. If the respondent is found in violation of this chapter, the Mayor may refuse to issue the respondent a license, may refuse to renew the license of the respondent, or may revoke or suspend the license of the respondent.
D.C. Code § 3-409