Real Estate Tax Abatement and Assessment

I recently received a letter from my Coop corporation stating the tax credit given to the corporation is much less than the credit they are required to pay each shareholder. So, the corporation decided that it's in their best interest to not issue a full credit to each shareholder. Additionally, the board of directors has voted to "assess each shareholder $1.35/share to offset the building tax abatement/credit." According to my monthly charges, my credit would have been just over $80/month. So, not only am I not getting my credit, but I am now expected to pay $250+ month for the next 6 months to offset the building tax abatement. Is this legal? And if so, can someone explain this to me?