In my opinion, letter of appointment is the replica of the contract of employment between the employer and the employee. Its requirement becomes essential, only when the contract of employment creates a substantial employment relationship for a considerable period which is predetermined.
Though payment of wages or salary is an important aspect of the contract of employment, mode of payment as well as its method of calculation is not a decisive factor to determine the status of employment i.e., whether permanent, temporary or casual.
Normally, if the payment of wages is done at the end of the day, such workmen are deemed as casual labor in which case their resumption of employment from the next day onwards is dependent on the availability of the work. Such a practice is followed in case of incidental works like loading, unloading, cleaning and the like. Thus the nature of their engagement being on the basis of availability of the work as well as its quantum, it becomes adhoc and coterminous with the completion of the work. Therefore, no appointment orders are required for such casual labor.
Another genre is the temporary workmen whose services are utilized intermittently or till such time the work requires additional hands. Such work may be of incidental or core nature lasting throughout the year intermittently. For such works people with required skills and experience may be engaged on temporary basis which can be compared to the erstwhile " badli workers " of the textile industry. Even in such case, appointment orders are not required; just the nominal muster roll is enough to record their attendance during the waged period so as to calculate their wages on daily basis.
By and large, my submission would be that issuance of formal appointment orders is mandatory only in respect of regular employment lasting till the predetermined age of superannuation and fixed term contract employment.