Deduction of PF on arrears of salary

An employee received salary in april,11 @ 5500/- basic salary and deposit the PF660/-. in the month of may compay increase the salary to 7000/- p.m. basic w.e.f. 01.04.2011. Company limit the PF deduction up to 6500/-basic salary.

in the month of may whether we deduct PF on6500/- or on 7500/- (6500/- for may + 1000/- on basic arrear of april).

please clarify ASAP.