It was refreshing to read your post that you as a landlord isn’t money grubbing and after an increase in rent when the lease is due for renewal. Restores ones faith in humanity. Usually, in my experience as a landlord, the tenant is asking for a drop in rent or they will go and rent elsewhere. I always agreed, as I didn’t want to go through the hassle and expense of advertising for and finding a new tenant, and then paying the agent their 110% commission on a weeks rent. I was just happy to have tenants who paid rent on time and didn’t trash the place.
Anyway, back to your question; while I am unaware of any legislation you can quote, it is unethical for the agent not to consult you on raising the rent. As the landlord, the ball is in your court since you own the property and what you want goes, and you can instruct her/him to reduce it back to the level it previously was, and that you require them to consult you on any issues concerning the property in future. If this causes dissonance in your relationship with the property manager then you can complain to their manager, or walk elsewhere and take your business to another agency to manage your property. Best to handle it diplomatically and request that the rent be restored to the previous rate, and you will consider an increase at the next lease renewal date but you need to be consulted first.