Shemiras Halashon Halachos
Hilchos Lashon Hara, chapter 1, section 3 The person who speaks lashon hara transgresses, "Do not go as a talebearer in your nation," if he speaks negatively of his fellow on occasion. But if, heaven forefend, he habitually transgresses this sin on a permanent basis, such as those who sit and speak negatively about people, they are called "baalei lashon hara" (habitual speakers of lashon hara) by Chazal and their punishment is far greater, since they transgress the Torah of Hashem out of denigration [of the Torah] and disregard the prohibition. Regarding them it says in Tehillim (12:4), "Hashem will cut off all flattering lips, a tongue that speaks proud things."
Hilchos Lashon Hara, chapter 1, section 4 Chazal say that for three sins one is punished in this world and does not have a portion in the next world. These are: idolatry, immorality, and bloodshed, while lashon hara is equal to them all [combined]. The Rishonim explain that Chazal refer to someone who is habituated to speak lashon hara constantly, due to it becoming as if permitted to him through much habit.