“This is a business,” Ms. Melling said. “At the end of the day, it sells services for photographing weddings. This is like putting up a sign that says ‘Heterosexual Couples Only.’”…

Most courts, to say nothing of serious photographers, agree that photography is expression entitled to First Amendment protection. Ms. Huguenin composes and selects images, arranging them in picture books that tell the stories of memorable days. But there are stories that she does not wish to tell.

Tobias B. Wolff, a law professor at the University of Pennsylvania who represents Ms. Willock and Ms. Collinsworth, said Ms. Huguenin had given up the right to make that choice when she opened the doors of her business to the public…

“A tattoo artist should not be forced to put a swastika on an Aryan Nation guy,” Mr. Lorence said. “The government could not force someone to put a bumper sticker on their car that says, ‘I support same-sex marriage’ or ‘I support interracial marriage.’ ”