Leave Application - Warning Letter

Please help me on this matter :
We are converted a practical student to permanent staff on 22 July 2013. After work for 1 month he was required back to the college to complicate their final presentation. The staff just send message to the Project Manager to inform his required back to college for 1 week to complicate presentation .
After 1 week later (today) , he sent the other message to the Project Manager again to inform his yet to done his presentation , he will continue stay at his college untill finish this presentation.
With above matter, could I send him warning letter ?
Thank you.
Celine

Prior making him permanent employee have your ever apprised him rules / regulations / terms / conditions of employement. If yes have you issued any appointment letter to him if yes please take necessary action with reference to Appointment Letter.....

I agree with Prashant - there must be some letter issued during the time of appointment stating terms. Based on that you should take the decision.
Thanks,
Deepa.
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Hello Celine,
Before you arrive @ any conclusion that the staff/employee should be penalized, have you made ANY efforts to check IF he was telling the Truth?
For all you know, MAYBE he was speaking the fact? Suggest First check this aspect before moving to do what you wish to do.
One way could be to call his College/Institution. Another way could be to talk to any other students from the same college who joined your company along with him.
In Principle, penalizing SHOULD BE THE LAST RESORT--NOT THE FIRST ONE when you deal with employees/staff of this level. After all, they are still raw & even if you would have informed him of the Rules/Policies, they would take time to get out of the student mentality to a professional attitude--give him the benefit of doubt.
Once you make the checks & IF you find evidence that he is misusing the trust reposed in him, then go for the tough measures.
All the Best.
Rgds,
TS

Hi all Senior,
Yes, I have issues him an Offer letter as permanent staff . I already when through with him the leave application process during orientation , supposedly he should know the process.
Besides that, I have called to his college 's lecture for verification and his lecture admin this is the final section for the student to complete it. That prove my staff who are telling me the truth but he failed to fulfill company policy of Leave application. Could I send him 1st warning letter to him ?
I plan to do that decision because of avoid other staff to follow his steps.
Regards,
Celine