Re: "Terms of Employment Act, 1994", changes to an employee's contract of emp.:email
"OP" means "Original Poster"
The point isn't really whether you can/should insist on a letter, but whether the employer can make this change unilaterally and without your consent. From the post you linked to, the company is seeking to make two changes to your terms of employment: (i) change in working hours and (ii) requiring you to be on call.
Does your contract of employment have a section saying that the company may require you to work different/additional hours as necessary/reasonable? (Normally they do) If it does, then I'd imagine that a change of an hour either way would probably be considered reasonable. The "requirement" to be on call would, to my mind, be a less reasonable change and would be more likely to require your consent, even if they offer more money for you to take on that additional responsibility.
When you went to flexitime, was that arrangement agreed in writing or did you just change over to flexitime without additional/different terms? If not, then your original contract would govern (9-5.30) and it would be difficult to refuse a non-agreed change on the one hand (moving to 8-16.30) but yet insist on a non-written agreement on the other hand (flexitime).
It's a delicate balancing act as your employer is probably introducing these changes to better run their business and doesn't appear to be targetting you specifically. As you have been there longer than a year, they cannot simply terminate you for questioning the changes. Rather than insist on the changes being put in a letter (which won't make any difference), if you have good reasons not to agree to the changes, I'd bring that up with your employer/HR and see what they say. I'd take the position that any of these changes do require your agreement and outline why you don't want to agree and offer to discuss alternative arrangements (e.g. you could work from home from 8am and then come into the office?). I'd also leave room in the conversation to accept the changed conditions in the end - if the employer is dead set on implementing these new conditions and you are dead set against them, things will get difficult for both of you and, although you may be in the right from a legal point of view, if they orchestrated a dismissal out of it, you might be left with an award in court, but no job afterwards...