"Dues to a subdivision HOA are voluntary, dues to a condominium association are compulsory". Is this true if the sub HOA is a 1965 nonprofit?

The question

I serve as treasurer for my subdivision and have 4 hard line "no's". The HOA was established as a nonprofit in 1965 by the warranty deed. The nonparticipating residents claim a real estate agent has told them dues are voluntary for a sub HOA. Is it true or is there a reference that defines when the HOA for a sub is voluntary or involuntary?