Most often formal disputes are started when a worker files an "application for mediation or hearing (Form WC-104A)." The law requires that this form include detailed information about the injury. At the time it is filed the worker must also provide the employer with any medical records relevant to the claim that are in his or her possession. When the application is received by the agency, it is sent to or "served upon" the employer and its insurance carrier. The employer must then file a Carrier's Response Form providing detailed information from its point of view and must send medical records in its possession to the worker or the worker's attorney.