Is there any spanish law that prevents me paying my community charge by monthly installments

Thankyou.
The community when formed 4 years ago agreed that community fees could be paid monthly by direct debit, the current president is now saying that if fees are not paid in full within 1 month of due date then an extra 20% default fee will apply. can this be done?

Thankyoy, Spanish Lawyer.
That information is very helpful.