I did try to call the Labour Department, they said it's up to my own discretion to decide if it is that serious. However, the agent said verbal warning is no use and we must issue warning letters to them. Also they said if the maid is going to sue me,then she will present the airticket which I bought for her and the issue date is 16 August, that means I have planned in advance to fire her but in order to avoid paying her the HK$3270, I issued the warning letters to her.
So I think you guys also have to bear in mind of this point.