Dear Kashif,
Yes, all the communication related to the matters of discipline or indiscipline should be issued under company's letterhead. It lends credibility to the communication.
Ningthoujam I: - There is nothing like letterheads should be used for external communication and communication sheets should be used for the internal communication. Where did you read this? Can you please provide any reference?
As per definition given in the Collins dictionary, continuation sheet is a page that continues from the one before it, containing similar information.
While communicating with external party or for internal communication, if the document has multiple pages then first is page is printed on the letterhead and from the second page onward, continuation sheet is used.
Generally printing cost of letterhead is higher than that of continuation sheet as unlike letterhead, it just has the logo of the company and nothing else. If second sheet onward if the continuation sheet is used then it saves the stationery cost. Hence it usage.
Thanks,
Dinesh Divekar