As many as 300,000 copies of the Bible and the Book of Mormon are expected to be placed in Sheraton, Westin, and other Starwood hotels by the year's end.
The Associated Press reported that Marriott International, which bought Starwood two years ago, has begun the process of adding in the Bibles, which are supplied for free by Gideons International.
The move is part of Marriott's initiative to put Bibles in the rooms of its 6,500 properties, a tradition that goes back to the late 1950s.
The company's namesake founding family is active in The Church of Jesus Christ of Latter-day Saints, which is why the Book of Mormon is added along with the Bible.
Marriott said in a statement that it does not receive much opposition to its hotel-room Bibles.
"There are many guests who are not digitally connected who appreciate having one or both of these books available. It's a tradition appreciated by many, objected to by few," the company argued.
Still, some secular organizations, such as The Freedom from Religion Foundation, have in the past campaigned against Bibles being distributed in hotel rooms.
In late 2015, FFRF advocated for all such Bibles to be replaced with copies of Charles Darwin's On the Origin of Species.
FFRF has accused Gideons International of "exploiting hotels and motels to proselytize a captive audience." The group sent letters to a number of hotel companies insisting that many people do not want to be exposed to the Bible on their travels.
"Those who must read the Bible every day will surely take precautions to travel with their own copies. The rest of us deserve a break from mindless evangelizing when we are on vacation," wrote at the time FFRF's Co-Presidents Dan Barker and Annie Laurie Gaylor.
"Many of your guests are freethinkers — atheists, agnostics, skeptics or 'nones' — who are deeply offended to be charged high fees only to be proselytized in the privacy of their own bedrooms. Not only that, the Bible calls for killing nonbelievers, apostates, gays, 'stubborn sons' and women who transgress biblical double standards," they told the hotels.
Marriott told AP on Sunday that there are some properties, such as its youth-focused Moxy brand and its luxury Edition brand that don't get Bibles in their hotel rooms, but argued there is no singular reason why.
"With any of our brands, there are hundreds of decisions made about the look and feel of the brand, how a room will be outfitted, what amenities it will have," the company explained.
Some foreign locations where Christianity is not the majority, such as Vietnam and Indonesia, are also excluded from the requirement of putting the holy book in their rooms, as it would be considered "inappropriate," the statement added.