Dec. 5 (UPI) -- The issue is whether Jack Phillips, the owner of Masterpiece Cakeshop, has a constitutional right to deny baking a cake for the couple.
Phillips, 61, has argued that his First Amendment right and artistic expression would be compromised if he made the wedding cake -- which he said conflicts with his religious views.
The five-year cake battle will ultimately test constitutional guarantees of free speech and religion against state laws that prohibit discrimination.
Charlie Craig, 37, and David Mullins, 33, the couple who were refused the cake by Phillips, already won at the Colorado Civil Rights Commission and the state Court of Appeals. However, the Supreme Court could result in a different outcome after the addition of conservative Neil Gorsuch in April.
On Tuesday, Justice Elena Kagan asked if the right to free-speech would extend to other businesses or artists including jewelers or hair stylists.
"How do you the draw the line?" Kagan asked.
Justice Anthony M. Kennedy said it would be an "affront to the gay community" if a baker or any business could advertise they refuse to serve LGBT persons.
ACLU attorney David Cole said "the only thing the baker knew was the identity of the customer" and they refused to make the cake not because of the message on it but because of their sexual identity.
At one point, Kennedy agreed with Roberts and Alito, saying, "Tolerance is essential in a free society" yet the state civil rights commission "has not been tolerant and respectful of Mr. Phillips."
The high court agreed to hear the cake case in June after Phillips lost a discrimination case against the couple.