The plans include scrapping a number of Coats of Arms created from shrubbery that were unveiled in 1961.
The civic movement LX Citizenship Forum said the project entails the “definite destruction” of the emblems, which it said is “a ridiculous attempt to re-write history.”
In a statement issued on Wednesday, Lisbon said the only Coats of Arms left in the garden are remnants of a temporary exhibition.
It reasoned that as heraldic designs were not included in the garden’s original project, the recently-approved proposal cannot do away with them.