Baronelle Stutzman was sued after she declined an order from a customer she had previously served for ten years.
The owner of Arlene's Flowers in Richland was given fresh hope last year when the US Supreme Court asked the Washington Supreme Court to reconsider the lawsuit against her.
This was as a result of cake-maker Jack Phillips winning a case in which he was told he was within his rights to refuse to make a cake for a gay wedding.
However, in a unanimous decision, the Washington Supreme Court's nine justices said that Stutzman had violated a state anti-discrimination law by refusing service to Robert Ingersoll and Curt Freed, for their 2013 marriage.
On Thursday, Washington high court again rejected Stutzman's argument that arranging flowers for a same-sex wedding would violate her free speech rights under the US Constitution's First Amendment and would be on par to endorsing same-sex marriage.
John Bursch, an attorney with the Alliance Defending Freedom, a conservative legal group that represented Stutzman, said the state has been hostile toward her religious beliefs. "We look forward to taking Barronelle's case back to the U.S. Supreme Court," he said.
Stutzman is being represented by religious freedom charity Alliance Defending Freedom (ADF).
Addressing the development, ADF attorney, John Bursch said: "We look forward to taking Barronelle's case back to the US Supreme Court."
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