A gay couple say a New Zealand baker refused to make them a wedding cake because of their sexuality.

Moe Barr and Sasha Patrick, from Brisbane, planned to get married in Waipu, Northland, in January.

They had organised to have a wedding cake made by Kaths Devine Cakes in Warkworth.

But the owner told them that would not be possible because same-sex marriage went against her beliefs.

Barr posted an email from the owner, Kath, on Facebook.

"I do not wish to offend either of you and I thank you for letting me know that it is a same-sex wedding," it said.

"Even though as individuals you are both fabulous and amazing people, I must follow the integrity of my heart and beliefs.

"Our government has legalised same sex marriages, but it is not my belief that it is correct, therefore I will not support it and cannot make your wedding cake for you."

Barr expressed disappointment on her Facebook page, saying :"Be sure to avoid Kaths Devine Cakes if you support marriage equality".

The business has been contacted for comment.

A similar case in the United States went all the way to the Supreme Court after a gay couple, Charlie Craig and Dave Mullins, complained of discrimination when baker Jack Phillips refused to make them a wedding cake.

The court sided with Phillips, but did not go as far as creating an exemption for businesses to refuse service to gay customers.