A Christian law firm is making a last-ditch effort to convince Arizona's Supreme Court that businesses — at least some of them — have a constitutional right to refuse to sell their services and products to gay people.

In new legal filings, attorneys for Alliance Defending Freedom are telling the Arizona Supreme Court that the U.S. Constitution protects not only the right of individuals to speak but also their right to not be compelled to say things they do not believe.

In this case, they contend that a Phoenix anti-discrimination ordinance is effectively telling Joanna Duka and Breanna Koski, the owners of Brush & Nib Studio, that they have to design wedding invitations for customers that "celebrate" same-sex marriages. And that, the legal papers argue, violates the religious beliefs of the "Christian artists."

Attorney Samuel Green told Capitol Media Services the pair are not refusing to sell to gays who want to wed. He said the studio has a variety of pre-made artworks.

But he said the issue is different when they are asked to create artwork in designing invitations and other wedding items to celebrate something that violates their beliefs.

"Art is speech itself," the legal papers contend. "And so a law compelling art compels speech."

The couple and their lawyers need Supreme Court intervention after the Arizona Court of Appeals rejected similar arguments, concluding that the Phoenix ordinance has nothing to do with speech.

Instead, the appellate judges said it simply regulates the conduct of those who offer their services to the public. And they said the studio's owners remain free to not only believe what they want about who should marry but to speak out and even post messages at the business about their beliefs.

What they cannot do, the judges said, is "use their religion as a shield to discriminate against potential customers."

The decision of the Supreme Court will have implications beyond the the Phoenix ordinance that makes it illegal for businesses that provide goods or services to the public to discriminate based on age, sex, race, color, religion disability, marital status, national origin, sexual orientation or gender identity or expression. It carries penalties of up to six months in jail and $2,500 in fines for each day business owners are found in violation.

Several other communities including Tucson, Tempe and Flagstaff have similar laws. And any ruling would govern whether other communities can adopt — and enforce — their own ordinances.

The key legal issue, Green said, is convincing the Supreme Court that there's a difference between refusing to serve gays, something his clients say they do not do, and forcing them to use their talents to craft a message contrary to their beliefs. He said the studio owners are "writing literal words."

"They do calligraphy, they do hand lettering and then they also do painting," Green said. He said there is a long line of court rulings which conclude that words and paintings are "pure speech."

What that means, Green said, is they are constitutionally entitled to refuse their talents to craft something that runs contrary to their belief.

He said this isn't a new concept.

Green cited a 2012 Arizona Supreme Court ruling which said that tattoo artists are engaged in "protected speech," and that gives them the right to refuse to ink a customer with a message that violates their beliefs, even if the customer comes in with his or her own words and simply asks the artist to tattoo that onto them.

"If a tattoo artist is engaged in pure speech, then certainly someone who is painting and writing designs on paper is also engaged in pure speech," Green said.

He said the legal issues here go beyond sexual orientation.

"If a Jewish synagogue came into a Muslim printer and told them what they wanted to say to promote the synagogue materials, it's still the Muslim printer that's going to have to speak a message they object to in creating those promotional materials," Green said. "No American, whether it be the Muslim printer or Joanna or Breanna should be forced to live and work and convey messages that contradict their beliefs."

Green rejected any suggestion that what his law firm is asking the Supreme Court to rule also would permit a business owned by those who do not believe in marriage between the races to refuse to provide services, including invitations, to interracial couples. He said people in the latter category are basing their views on "white supremacy."

"These are people who are not willing to serve everyone," Green said. "Our clients serve everyone. They just can't express certain messages that violate their convictions."

In writing for the appellate court last month, Judge Lawrence Winthrop said no one is seeking to infringe on the free speech for the two women.

"They may post a statement endorsing their belief that marriage is between a man and a woman," the judge said. "Or they may post a disclaimer that the act of selling their goods and services to same-sex couples does not constitute an endorsement of their customers' exercise of their constitutional right to marry or any other activities."

But he said that if they want to operate their for-profit business, they cannot discriminate against customers based on their sexual orientation. And Winthrop rejected their claims that the ordinance substantially burdens their religious beliefs.

"Appellants are not penalized for expressing their belief that their religion only recognizes the marriage of opposite-sex couples," he wrote. And he said they are free to refuse to create wedding-related merchandise for same-sex couples, but only as long as they refuse to provide the same service for opposite-sex couples.

The Supreme Court has not set any date to consider whether to hear the case.