What should I do if I think one of my employees is always late?
If you don’t have evidence, just perception, introduce a process (it doesn’t have to be complicated or expensive) that means everyone has to sign in and out each time they enter or leave your premises, including at lunch time. Treating everyone equally means you will be able to identify those who are regularly late and will have the evidence with which to progress the matter if necessary. It also means you have an accurate record of who is present in your premises in the event of a fire.
How do I deal with an employee who is regularly late?
An informal meeting should be held first to make the employee aware of the problem and to give you an opportunity to talk to them about any possible reasons, for example a change in school that is further away may mean they arrive consistently 5 minutes late. Look for ways you can accommodate this, for example by amending the workers hours. Make it clear what you expect from your employee and what might happen if they fail to meet your expectation.

