As per section 2(22) of ESI Act, 1948 the term 'wages' includes all remunerations(except as specifically excluded in said section) paid or payable. Hence, contribution on arrears of wages is also payable under provisions of said Act.
However, in my opinion, the contribution on such arrears is payable since the date when such revision in wages is announced or wages are reported pending for payment.
Before, however to be on safer side, taking final decision in the matter it will be more appropriate if matter is taken up with the appropriate Regional Office of ESIC of your area for decision in the matter so that at the time of inspection of records, such omitted wages are not pointed out by the Inspecting Officer.
For calculating period of contribution kindly see section 2(23) of said Act which defines 'wage period' as the period in respect of which the wages are ordinarily payable in respect of an employee.
Harsh Kumar Mehta
"As and when any increase in the wages/ remuneration is declared with retrospective effect, the liability towards payment of contribution accrues only in the month in which the decision is announced and no contribution is payable on the arrears pertaining to the period prior to the month of declaration/ announcement".
2.However contribution is definitely payable on annual/periodical incremental arrears which is declared belatedly
ADVOCATE & LABOUR LAW ADVISOR
Labour Law Adviser