A termination notice period of 2 weeks is very short for someone in a sensitive position. Nevertheless, when you say "effective immediately", I presume you mean he leaves immediately and does not work out his notice period, but you pay him for that period.
This is definitely allowable (legal).
Alternatively you may be able to direct him to remain at home for the notice period and not commence his new job during the notice period, while he is still effectively in your employ. Although it may be argued that you can only do this is if there specific "gardening leave" clause in his contract.
You can of course require him to work out his notice period and have him do a different task whereby he has no access to sensitive information.
This article by the law firm Middletons sums up gardening leave nicely and highlights some potential issues for Victorian employers.