Increase in interest rate without warning

Good morning all,

This is a question for the legal experts..
I got two investment mortgages through Westpac in November 2015, both variable.
One was 4.28%, the other was 4.55%, I just logged on right now and have discovered that both loans are now 4.75%. I am aware that banks are increasing their rates for investors but can they increase them without notifying their customers first? I received nothing in the mail, no phone call, no email etc.

Obviously there is little I can do but surely there has to be something that warrants notification first? Is that even legal to raise rates without notifying your customers first?