Although it is uncommon that expert panelists are asked to testify at a hearing, when they are asked to testify, they must comply.
Most expert panelists are never asked to testify, and are not required to do so.
If expert testimony becomes necessary because of the circumstances below, the expert panelists are asked if they would like to testify as an expert witness. If an expert elects not to testify, the agency will attempt to find another expert to testify.