Barronelle Stutzman, 72, from Washington says she will take her case to the national Supreme Court after the most senior court in the state upheld an earlier ruling that she had discriminated on the basis of sexual orientation.
Alliance Defending Freedom (ADF), which has been supporting Stutzman, said: "Barronelle's story demonstrates a troubling trend - governmental agencies and officials that have grown increasingly hostile to religious freedom, particularly the freedom of people who believe that marriage is the union of one man and one woman.
"These widespread efforts to suppress freedom are rooted in a disdain for this particular religious belief - a belief that, in the words of the U.S. Supreme Court, is 'decent and honorable' and held 'in good faith by reasonable and sincere people'."
(Above: A video by ADF)
Stutzman received a warning later from Washington's attorney general after she refused the order at her store, Arlene's Flowers, in Richland in 2013.
The situation escalated when the American Civil Liberties Union and the state of Washington successfully sued her for discrimination, prompting Stutzman to appeal.
Upholding that ruling, the state's Supreme Court on Thursday agreed that Stutzman violated law, stating she must abide by state anti-discrimination laws regardless of her religious beliefs.
The court was quoted by the Catholic News Agency as concluding: "We therefore hold that the conduct for which Stutzman was cited and fined in this case - refusing her commercially marketed wedding floral services to Ingersoll and Freed because theirs would be a same-sex wedding -constitutes sexual orientation discrimination..."
ADF added: "Barronelle ...serves everyone in her community, regardless of their race, sex, religion, or sexual orientation.
"But even though she serves all people, she cannot use her artistic skills to celebrate all events.
"In particular, because of her beliefs about marriage, she cannot design custom floral arrangements for a same-sex wedding (although she would be happy to sell pre-made arrangements or raw flowers to couples planning such an event)."