Dear Lakshmanan,
Engagement of a labor law consultant for your establishment depends on factors like nature of activity, no of workmen, existence of trade unions and its impact on industrial relations etc. Routine compliance works like preparation of wage bills, periodical payments to statutory authorities like ESI,EPF etc., maintenance of registers and records, filing of periodical returns etc should be done by in-house persons. Matters relating to disciplinary cases which have legal consequences, changes in service conditions, certification or amendment to standing orders, implementation of minimum wages, fixation of bonus etc., revision of wages and negotiations in this regard are matters involving the guidance of a consultant having experience in labor laws and industrial relations. Of course, if your HR head is well-conversant with labor laws and industrial relations and can guide his team properly, no necessity for a consultant.
In my opinion, you can have a consultant on retainer basis so that he can have a thorough idea about the industry and guide you then and there.