A family member, who did not want to be named, told Newshub he and his family had driven from Timaru to the restaurant in Oamaru specifically for the occasion.

He said they had brought the birthday cake because they were unaware of the restaurant's no BYO cake policy.

"The lady serving us was really weird about it when we turned up and said she would ask her boss. I said not to worry and just to put it out the back until we left and that's what we did. We didn't even eat it there," said the family member.

He said he wasn't aware of the post until the following morning.

"I was pretty shocked and disappointed when I saw it and commented because I was hacked off."

He said the family had accepted Mr Smith's apology but won't be returning to the restaurant again, despite enjoying it in the past.

"I'm just annoyed it happened full-stop. I think it was a pretty embarrassing thing to do.

"He [Mr Smith] said it wasn't intended to embarrass but that's complete rubbish," said the family member, referring to the language used in the post.

Mr Smith said the post was a spur-of-the-moment decision in response to a "bug-bear" that he had about people bringing their own food.

"It starts an awkward moment. We're trying to be a professional, high-quality establishment. We have our own cakes people can purchase."

He said cakes were a grey area for some people because of the emotional energy involved in making them.

Despite what happened Mr Smith, said the restaurant's no BYO cake policy would remain.

"You don't go into a bar expecting to bring your own drinks; a restaurant's the same for me. A cake is still food."

Mr Smith said he expects there will be implications for his business but that he is prepared to pay the consequences of his actions.

"I'm sure there will be repercussions but that's not my main concern.

"All we can do is learn from it and come back to work the next day and keep going."

Newshub.