One kind reader sent me an email suggesting that describing prayers to the departed saints as "idolatrous" is a novelty in view of the testimony of Scripture.
The term, "idolatrous," is not the best word for the sin. Nevertheless, surely the novelty is the practice of praying to anyone but God. Attempts to contact the dead in various forms have been constantly opposed by Scripture:
Leviticus 19:31 Regard not them that have familiar spirits, neither seek after wizards, to be defiled by them: I am the LORD your God.