A scary comment to hear from anyone, especially my clients.
Why? Because there has been no such thing as a verbal warning since 2009!
If staff are not doing what they ought to, then you need to have an informal chat with them. Remind them what they should be doing, e.g. coming to work on time. Find out if there are any reasons why that is not possible (!) and agree with them what is going to happen so that they can do what they are supposed to.