Disciplinary Route. Failure to cooperate with the employer in fulfilling his statutory duty. Failure to follow reasonable instruction.

I agree with Ron. You don't have to make it part of their contract of employment - complying with HASAW section 7 is compulsory.

Wholly agree with JohnMurray - your first port of call has to be to find out why they are refusing to attend the appointments. I encountered similar issue a number of years ago and it was the employees perception that by attending these appt's it meant the employer would be given access to all their medical history/data which they weren't happy about (fair enough I wouldn't want my employer to see mine). We got a sample certificate of fitness from the OHP that showed the what a typical certificate of fitness would look like, including one which highlighted an area of concern such as a hearing issue or colour vision issue (this was important to us at the time) and this made the world of difference. Yes if all else fails you can go down the disciplinary route but this might not make any difference and you could potentially loose good employees so try every other avenue first.