Is it obligatory to place salt on the table or is it a Minhag?

The Rema (OC 167, 5) writes, it is a Mitzvah to place salt on the table since the table resembles the altar and all the sacrifices had salt brought with them; he also adds it acts as a protection from punishments. Clearly this is a Minhag and not an obligation yet the Aruch Hashulchan (167, 12) adds that all G-d fearing people follow that custom.