If employees are leaving the job all of sudden, then it is called as abandonment of employment. They are taking undue advantage of not having proper HR systems and process. HR systems and process are there or not, what matters is mental engagement of the employees with the organisation. Your problem is this mental disengagement.
You may check the terms and conditions mentioned in the appointment letter. If nothing is mentioned, then issue a letter to each employee stating that while separating from the organisation they must give two months notice. Else they are liable for the disciplinary action. Those who abandon their services, do not issue them any "Service-cum-Employment Certificate".
Employee attrition is a result of flaws in the organisation's culture. To understand these flaws, the first step is to study the causes of attrition. For this you need to do attrition analysis. Earlier, I had given exhaustive reply about attrition analysis. Check the following link to refer it:
Conduct the analysis on the points mentioned in the above link. After that you may come back to seek further advice.
Work for some time,keep looking for other jobs and quit without any botheration or procedure.
Is your salary structure or working conditions below par?
What terms and conditions do you offer to employees in the appointment order?
Does it speak of exit rules-notice period,whether notice can be purchased etc??
You have to take a holistic view to find out why employees are literally abandoning jobs in your company and lay a framework of rules,procedures,employee engagement techniques to stop the sudden outflow of employees.
Attrition will cost you heavily in terms of loss of productivity,looking for employees,recruitment and training costs etc.
A clause in your offer letters is a step to stem attrition, but you need to make fundamental changes by analysing reasons for frequent exits.
1.Shri Nathrao & Divekar rightly pointed out remedial action to be taken.
2.It give bad name to Organisation as une employee add / put fuel and spoil the image of Organisation .
3.Take remedial action on time .
4.Consult / Take advice of expert s in this field.