Is it legal to charge 6 months late fees for one missed payment?

I have always paid my HOA fees, but last June I went on vacation and completely forgot to pay.

At that time, the HOA office was going through some difficulties and did not send out late notices, Now, after 6 months, they hired a company to do the books.

They sent me a notice that I missed that one payment, and attached 6 months of late fees. Is this legal? Had I known I missed the payment, I would have sent it immediately.