Basically Form 16 is meant for the declaration/certification that a certain amount is paid to employee as salary & tds has been deducted on that under section 192 B of income tax act. Thus if there is no tds that it is not mandatory to issue the tds certificate(Form-16) however employer on its own discretion may issue nil tds form. In such type of cases instead of the form 16 employer should issue salary certificate.
I am not agree with Mr. Abhishek's view for the second part. What he is saying that form no. 16 is certification by the co., is right. But instead of Form No. 16 Just a certificate from the co. is not right, The co. must issue Form No. 16 stating that the employees income is not taxable & hence no TDS is Deducted.