OUTSYED THE BOX
The question is since when can a political party summon (even by way of a letter) any Government Department for a meeting? This is procedurally incorrect and for the Government Department concerned, it will be administratively incorrect too.
No Government Department in the world (JAIS is a Government Department) can be called, invited or summoned by any private entity - especially a political party - to attend a meeting to explain THEIR actions. It is always the other way around - the Government Department can call anyone relevant to attend any meeting.