If company stopped giving year end bonuses since 2008 can we still sue them this year (2013)?

Atty. good day to you.

I work in a big company(well known) here in the philippines and since 2008 they unilaterally stopped giving year end bonuses which they usually give aside from the 13th month pay that they provide to supervisors and rank and file employees.

The bonus that they gave before 2008 vary from as little as Php4000 across the board to as high as 75% of the basic salary of every employees. However, starting 2008 they just unilaterally stopped giving the said bonuses citing low operating income as an alibi (managers are still receiving annual incentive bonus worth hundreds of thousand of pesos but not the supervisors and rank and file employees).

My question is would this already be a classic case of diminution of benefits? If it is can we still sue the company this year (2013)for not giving this bonus from 2008 to 2013 to the supervisors and rank and file employees?

thank you so much for any advise that you can give.

i think it's too late and on its face, it seems to be management prerogative, but you can file a money claim at nlrc but it will cover only last 3 years

thank you for the response attorney. just a brief background about my company.

they've been giving christmas bonus on top of the 13th month pay for decades now. only last 2008 did they stopped giving such bonus. my own understanding and our union's understanding as well is that this has already morphed into a benefit? is this correct.

another issue regarding the diminution of benefits is that recently 2 of our new union members where deducted Php550 pesos each by the company and the justification stated on their payslip is "SALARY WAGE DIFFERENTIAL".There are no further explanation from our HR as to why they are being deducted. is this legal?

thank you so much!

again, you feel you have been unduly deprived, then the remedy will be first through your CBA mechanism