Grainne McCann, a London-based woman from Northern Ireland, told the Belfast Telegraph that she ordered and paid for the cake online, but the order was rejected the next day.
"The wording we requested was 'Gay marriage rocks! Happy engagement, Andy and Joe! Lots of love xxx'.
"We were thrilled when Ashers accepted our online order, and full payment of £23.40 plus £20 post and packing, but the next day they sent the cancellation note and a refund," McCann said.
The bakery came under scrutiny in 2014 Gareth Lee, a homosexual activist requested for a cake with "Support Gay Marriage" to be written across it in icing.
The family-run firm, based in Belfast, refused to make it, arguing the cake's message was inconsistent with their deeply held religious beliefs.
They lost the case and their appeal after with a judge ruling at Belfast's Court of Appeal that the bakery had been guilty of illegal discrimination.
Delivering the appeal judgment, Northern Ireland's Lord Chief Justice Sir Declan Morgan said: "The fact that a baker provides a cake for a particular team or portrays witches on a Halloween cake does not indicate any support for either."
McCann who ordered the cake for his friend Joe Palmer, said: "My gut instinct told me the cake was refused because it celebrated gay marriage."
McCann decided to order a christening cake for her goddaughter to prove this.
"Ashers couldn't have been happier to make that cake.
"A woman from the company even offered to drive it to its destination in Dublin as a favour, because she was going that way.
"This was terribly kind, but I felt angry and sad that Ashers' attitude to gay people is so different," McCann explained.
Palmer, who is marrying Andy Wong this summer said: "Thank God I live in London, where I can't imagine something like this happening.
"I'm staggered that Ashers wouldn't make the cake."
Daniel and Amy McArthur of Ashers Baking Company haven't released any comments about the accusation.
McCann eventually got the cake made elsewhere and said: "In my view, by turning away business based on the sexual orientation of the consumer they risk being sued again.
"My friends and I don't want to sue - Andy and Joe want to focus on their forthcoming happy day - but others might want to take action."
On the Ashers Baking Company's 'build a cake' section of its website the company outlines its terms and conditions.
Images and content are banned which contain "any threatening, defamatory, blasphemous or pornographic material, or show any kind of child abuse, or are racially offensive or abusive of any religion, or likely to incite hatred against any person or group, or are otherwise criminal or offensive in the minds of reasonable people, or are obscene or menacing or harassing in any way, or breach any applicable law".
