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Conservative Christians and Muslims differ theologically, but with regards to sexual morality they share a  common concern: Pornography.

In a jointly-authored letter, Christian and Muslim scholars are calling on the CEOs of Hilton, Hyatt, Marriott, Choice and Starwood hotels, urging a ban on adult entertainment in rooms... as "...a commitment to human dignity and the common good."

Dr. Robert George, the McCormick Professor of Jurisprudence and Director of the James Madison Program in American Ideals and Institutions at Princeton University, co-authored the letter with Shaykh Hamza Yusuf from Zaytunga College.

George says, "Instead of trying to move people by protest and demonstrations and threats of boycotts,  we make a simple appeal to the consciences of the corporate executive whose businesses have gotten into pornography."

Dr. Suzy Ismail, of the Center for Muslim Life, agrees, saying, "It would show that people are willing to take a stand against something that is morally wrong, despite the affect it might have on their profits, despite the affect it might have on whether or not people would go to these hotels."

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The porn industry is a multibillion-dollar business, raking in $57 billion annually worldwide, $12 billion of which is in the United States. According to the 2004 IFR research, porn revenue is larger than all combined revenues of all professional football, baseball and basketball franchises.

Steve Hirsch of Vivid Entertainment, one of the largest producers of pornography, says porn is not going anywhere. And if people don't want to watch they can tune out.  "These groups, these sort of self-proclaimed morality police,  they come in and want to tell you what's the best for you to watch and it never works."

Fox contacted all five hotels requesting interviews. Starwood and Hyatt Hotel have yet to respond. But in a statement, Hilton Hotel said,

"All adult content is only accessible to adult guests who request access and choose to view it."

Hyatt Hotels says, "We make it easy to block adult content in the room, which must be selected and paid for separately from all regular television channels. We also take steps to ensure that guests will not be inadvertently exposed to this programming."

Choice Hotels are independently owned and operated,  and said the entertainment options are left to owners.

But George says that's no excuse.

"What Choice ought to be doing here is, at a minimum, making clear to the franchises that they don't like the idea of pornography in hotel rooms that have the name of Choice... That they as a matter of conscious, don't believe it's proper."

Marriott appears to be heading a new industry trend. It says it is working on removing on-demand adult content by switching over to an Internet-based system. Guests can access porn that way, but the hotel will not be directly providing it.

It's a bottom line decision, because statistics show that the Internet is where people are increasingly watching their movies, including pornography.  A  2011 report by PKF Hospitality Research found that from 2000 to 2009,  revenues from hotel movie rentals in general decreased 39 percent.  Personal computers and access to WiFi has opened up a wide variety of ways to watch films.

It's a change dictated by the market, not morality. A fact that fuels future fights by religious conservatives.  Ismail says, "There's a point of view that you can either speak out against what's wrong  or you can stay silent. And if you stay silent, "it is "a sign of agreement."