Is it legal to charge a late fee on a late fee?

[jmbw]

I live in an unincorporated subdivision, which means I have an association. We understand we don't have the same privileges as incorporated towns and have to pay addional costs for things they wouldn't. My association decided to re-pave all of the roads in our subdivision. We didn't agree it was necessary as they were still in good condition and because the cost would be our burden. Despite many others agreement, the association had enough votes to pass the 'improvement' and it was done at a cost of $400 per lot. We have two lots, so our cost was $800, payable immediately upon notice of the passing. If it was not paid within 60 days, they would start assessing late fees on the amount owed. I am the sole supporter of a household of five and it took several months for me to be able to pay it. I paid the $800, but not the $80 late fee they had already added by then. They have begun adding late fees to the $80 and billing me for this. The late fee is 1 1/2% of the balance owed per month. Is this legal? If not, how do I stop it?