Dicta of Mason J (as he then was) in Rochfort v TPC  HCA 66; (1982) 153 CLR 134 is that in some cases it may be appropriate to subpoena an employee directly rather than the employer (as would be the usual practice), having regard to ‘the efficient administration of justice’.
Recognition of these interests of the employer suggests that in general it is he, not his employee, who should be required to produce the documents. Of course, the protection of the employer’s interests must give way to the public interest in the efficient administration of justice in case of collision between the two. So if it is impracticable to serve a subpoena on the employer, e.g., by reason of absence overseas, incapacity or his whereabouts, being unknown, the court will insist on production of the documents by his employee or agent who holds them. In these circumstances the prompt dispatch of court business must prevail over the protection of the employer’s interests. (at p145)