23 June 2021
There is no way in which an ordinary citizen could be compelled to attend a departmental inquiry unless the IO is duly authorised under the provisions of the Departmental Enquiries (Enforcement of Attendance of Witnesses and Production of Documents) Act.
However, to my knowledge, this procedure is seldom invoked. A Government employee is liable for disciplinary action in case of refusal to appear.
25 June 2021
It is not mandatory for the inquiry officer to summon the witness constantly if he is not appearing before the inquiry committee. The reasonable number of summons can be twice before the inquiry officer is dispensing with the attendance of the said witness and endorses his report about the circumstances under which he dispensed with the personal attendance of the witness.