Arduin supplement Arduin Grimoire Volume 6: House of the Rising Sun. The vicious deity Sunsagora is extremely evil and her worshippers castrate males and burn them alive. As a result, her worship is forbidden almost everywhere in Arduin.
In the Theocracy of the Pale, the only legal religion is worship of Pholtus. All other religions are forbidden.
In many areas, religions based on evil deities are officially forbidden because of the death and destruction their worshippers tend to cause. Chief among them is the worship of Tharizdun, due to him being an Omnicidal Maniac so evil that even the other evil deities cooperated to trap him. His worshipers tend to be trying to free him.
Greyhawk Adventures supplement. Incabulos is a Neutral Evilinvoked deity whose worship services are carried out in underground or remote forest areas to avoid detection. His priests are secretive in order to avoid those who hate evil. The temples of the Neutral Evil deity Nerull operate secretly in underground vaults to avoid the authorities because his ceremonies often involve Human Sacrifice.
Several countries in Faerun outlaw the worship of Talos (not to be confused with the Elder Scrolls deity), the god of storms, destruction and natural disasters.
Supplement FR1 Waterdeep and the North. The city of Waterdeep forbids belonging to any religion that kidnaps or sacrifices living beings, steals their property, or carries out attacks on non-worshippers. Due to the prevalence of devil-worship and similar cults among the aristocracy, enforcement is pretty spotty.
Supplement Forgotten Realms Adventures. Temples and shrines of the Neutral Evilinvoked deity Cyric are not tolerated in most cities. They're only allowed in Evil-aligned or very tolerant areas. Churches of the Lawful Good god Ilmater are ruthlessly persecuted by the authorities in Evil areas such as Zhentil Keep and Mulmaster.
Supplement Ruins of Zhentil Keep area card "Secret Temple". Temples of Bane, God of Tyranny, and Cyric, God of Strife, in good-aligned lands are hidden from view because their followers know that the governments of those areas would attack the temples if they knew where they were.
Polyhedron magazine #131 article "Pillars of the Realm". Religions that have an Evil Character Alignmentinvoked are forbidden in the city of Ravens Bluff. The religious order of knighthood called the Pillars of the Realm try to discover evil religions operating within the city and deal with them.
The Church of the Silver Flame rules Thrane as a theocratic state, and while religions like the Sovereign Host are allowed within its borders, their adherents find life less comfortable, and few other religions, particularly the Blood of Vol (whose association with the undead is utterly abhorrent to the Church), survive for long.
The only religion allowed within the confines of Riedra is the Path of Inspiration.
Imagine magazine Special Edition, which explains the Pellinore campaign. In the County of Cerwyn, the Council of Guardians does not tolerate Chaotic (Chaotic Good, Chaotic Neutral, Chaotic Evilinvoked) religions.
Polyhedron magazine #33 adventure "The Sword and the Anti-Hero", which is based on Finnish Mythology. In the land of Kittala, all of the religions of the land of Pohjola (such as that of Loviatar, the Maiden of Pain) are forbidden.
Ironclaw: Two of Calabria's four major houses have outlawed their ancestor's pre-S'allumer faiths. House Avoirdupois drove the Heliodromencer's underground some 700 years ago while House Bisclavret's "savage" cousins in the Phelan tribes still follow the Druids out beyond the reach of the Church and its' fanatics. There's no real trace left of whatever House Rinaldi worshiped before Saint Helloise came to them, while House Doloreaux never converted as a whole and still practices the old faith of Lutarism.
Mindjammer: The New Commonality of Humankind has not only banned most religions, but also memes such as democracy, communism, fascism, and "the Transmigration Heresy". Despite the whole "collective memory" thing and the fact that the Commonality is basically a communist dictatorship.
Razmiran outlaws worship of any deity but their god-king Razmir within the nation's borders.
After a particularly long and bloody religious Civil War, the nation of Rahadoum outlawed all religion and divine magic within its borders.
The worship of the Destroyer Deity Rovagug is banned pretty much everywhere for very good reason: his cultists are trying to free him from his prison so he can destroy the multiverse.
In Taldor, the worship of the Neutral Goodinvoked sun goddess Sarenrae was outlawed for decades because of politics. Sarenrae is a solidly benevolent deity, but she's also the patron god of Taldor's greatest rival, and the Taldan emperor worried that the faith harbored treasonous foreign influences.
Averted with worship of Asmodeus for the most part. No one really likes him or his worshipers. But even the Good Aligned Gods will admit that Asmodeus at least will work with you without backstabbing you if things get dire enough. And that he does give out good, if suspicious advice. It helps a lot that his worshippers will follow the letter of the law, if not the spirit.
Rocket Age: On Mars, the chief religious order, the Orthodox Fellowship, considers every other Martian religion or sect heretical and illegal. Whether their influence actually spreads that far is debatable, but they enforce their bans as much as possible.
Shadowrun: The elven nation of Tir Tairngire banned the Universal Brotherhood cult within its borders. They had good reason to: the organization in question is devoted to converting human beings into insect spirits. Aztlan revoked the Roman Catholic Church's tax-exempt status in 2027 and then outlawed it in 2041, in order to promote Aztechnology's Aztec revival religion. Yes, they banned Catholicism in what used to be Mexico. This has gone over as well as expected.
In the backstory, the Emperor outlawed all religion during the formative years of the Imperium (except for the Cult Mechanicus, because the Mechanicum was necessary and their religion was probably deemed "acceptable"). He promoted state-enforced atheism, publicly because religion was a superstition and a hindrance, privately because he hoped to quash Chaos Cults an attempt to starve the Chaos Gods to death. Unfortunately, it didn't work due to a research failure on his part: the Chaos gods are fueled not by prayer, but by emotion. A galaxy at war was great for the Chaos Gods in the short term, but they knew they had to do something and banded together to break the Imperium.
As a corollary to the above, the Emperor sent his "sons" to unite the galaxy into Imperium. One of them, Lorgar of the Word Bearers, chose to evangelize the cult of the Emperor in spite of his father's decree against religion. After a time, the Emperor publicly and painfully censured Lorgar, who turned to his homeworld's old religion which followed Chaos, and it was enough of a foot in the door for Chaos, but that's another story. Ironically, the illegal Imperial Cult started by Lorgar was institutionalized shortly after the Emperor's "death". Other religions are still ruthlessly suppressed.
There are actually countless variations on the cult of the Emperor, as establishing a single version on the million worlds of the Imperium is impossible. Instead, whether or or not a particular cult is heretical or not is basically up to the local governor/Ecclesiarchy, and the Inquisition intervenes if they think they're getting too lax. This has the unfortunate side effect of allowing genestealer cults to flourish under certain circumstances, as unlike Chaos cults, who are dead-set on toppling the Emperor and whose acts are rather obvious, the genestealers are allowed to keep worshiping a bastardized version of the Emperor as a father figure, which then leads to the Tyranid fleets attacking.
For the most part, only the cults of Chaos are outlawed by the church of Sigmar, as most other religions have non-Always Chaotic Evil gods (for example, there's a Friendly Rivalry between followers of a War God and a bear god). There are, however, occasional bans on specific cults and their practices for even non-Chaos gods, although they are predominantly imposed by the Empire's secular authorities: good examples would be cults of Khaine, a particularly dangerous war god to the High Elves, god of murder and assassination to everyone else; cults of Nagash, the Lord of Undeath (even before his ascension to actual godhood, there were a few); the cult of Stromfels, a god of piracy, sea monsters, and rule of force by the strong over the weak; and those who worship Ranald, god of luck, in his aspect as the patron of gamblers, swindlers and thieves tend to find their actions curtailed. Those that worship Ranald in his aspect as Handrich, god of merchants and commerce, don't have that problem.
In neighbouring Bretonnia, the official position is that only the state religion, venerating the Lady of the Lake, is an actual religion, everything else is peasant superstition to be wiped out when the local lord deigns to notice. However, the majority of peasants worship Shallya, goddess of mercy and healing without interference from their overlords, anyone from outside the kingdom is permitted to worship any non-Chaotic gods as they wish (on the grounds that "foreigners don't know any better"), and the coastal towns and cities worship Manann, god of the seas as a pragmatic defence against storms and tidal waves.
Warhammer: Age of Sigmar is similar to the situation in Fantasy; Chaos cults are still outlawed (and have an entire organization dedicated to rooting them out) as is worship of Nagash, the God of Death (other, less troublesome death gods, like Morrda, are allowed). Aside from them, the Cities Of Sigmar tend to be surprisingly religiously diverse for an empire with a literal God-King, with temples to Teclis, Tyrion, Allarielle, Grungni, Malerion, and even Morathi being common sites.
