Dear,
First of all, you have to determine what category of employee they fall under. If they are in the workmen category and you terminate them after issuing a memo, then you will definitely lose the battle in court.
If they are in the workmen category, then you have to provide them with an opportunity to explain themselves in accordance with the principles of natural justice. Issue them a charge sheet, ask for an explanation, and if you are not satisfied, then conduct a domestic inquiry. After the inquiry report, if they are found guilty, impose appropriate punishment.
Another critical point to consider is the gravity of the offense when giving out punishment. For a minor offense, you cannot terminate someone's services.