When can an employer insist that an employee see a doctor of its choice?

See Blackadder v Ramsey Butchering services Pty Ltd [2002] FCA 603 and in particular the following:
“ An employer has, as indicated above, strict obligations under the NSW legislation to ensure the safety and well-being of its employees. The importance of occupational health and safety is also reflected in the Act. Whilst an AWA, in general, prevails over conditions of employment specified in State laws to the extent of any inconsistency, provisions which relate to certain matters, such as occupational health and safety, operate subject to any relevant State law (see s 170VR(2) of the Act).
It is, in my opinion, essential for compliance with the above duties, that an employer be able, where necessary, to require an employee to furnish particulars and/or medical evidence affirming the employee’s continuing fitness to undertake duties. Likewise, an employer should, where there is a genuine indication of a need for it, also be able to require an employee, on reasonable terms, to attend a medical examination to confirm his or her fitness. This is likely to be particularly pertinent in dangerous work environments. Abattoirs entail obvious risks, among other things, of injuries from the repetitive use of knives at speed, and to the spinal column from the necessity to twist, bend and/or lift.
The question whether it is reasonable for an employer to request an employee to attend a medical examination will always be a question of fact as will the question of what are reasonable terms for the undertaking of the medical examination. The matters will generally require a sensitive approach including, as far as possible, respect for privacy. Nevertheless, I assume that there now should be implied by law into contracts of employment terms such as those set out in the first two sentences of the preceding paragraph, on the basis that such terms pass the test of “necessity” accepted by McHugh and Gummow JJ in Byrne v Australian Airlines Ltd [1995] HCA 24; (1995) 185 CLR 410 at 450.”