Dear Susheela,
Rather than jumping directly to the warning letter, I recommend you counselling him once or twice. Keep records of your counselling. Issue warning letter only if he does not improve after counselling.
How senior you are? I ask this question because counselling has to be done by some senior person. Just because you are from HR, your function does not give authority to counsel. Secondly, competence in counselling also matters.
Yes, nothing wrong in issuing warning letters as such. However, it would be tantamount of using hammer to affix a pin to few papers! Always keep in mind principle of
progressive discipline.
In case if he receives warning letter without counselling, mentally he may put off. It is not in the interest of organisation to have any mentally disconnected employee.
By the way, why is he talking too much? How come he has disposal time for this activity? Have you done
workload analysis of his job? Does he have sufficient workload? Increase his workload. Secondly, just explore possibility of sending him out of office for some field work.
If he is talking too much then he could be committing errors in his job as well. How is his quality of work? While counselling, in addition to garrulity, include this point of "inferior work quality" if it is feasible.
Ok...
Dinesh V Divekar