A Christian-run bakery is to face legal action over its refusal to create a cake featuring a pro-same sex marriage slogan.

The Equality Commission has confirmed that it is taking Northern Ireland-based Ashers Baking Company to court because it declined the order from a pro-gay activist in Belfast. It warned the company that it could face a sexual orientation discrimination case.

In a letter sent to the bakery last week, the Commission warned that it would start legal proceedings unless the company acknowledged that it had been in breach of the law. It said that "the claimant will be seeking only modest damages for the upset and inconvenience caused", but warned that "failing this, a civil bill will be issued".

The commission said yesterday that it had now received a reply from the bakery's solicitors "stating that their view remains unchanged, that their clients have not acted unlawfully".

It said that the case "raises issues of public importance regarding the extent to which suppliers of goods and services can refuse service on grounds of sexual orientation, religious belief and political opinion".

Daniel McArthur, manager of Ashers, said they would not be forced to promote a cause which goes against their conscientious view that marriage is between a man and a woman.

"We feel that the Equality Commission are pursuing us because of our beliefs that marriage is between a man and a woman", he said.

"It feels like a David and Goliath battle because on one hand we have the Equality Commission who are a public body, they're funded by taxpayers' money, they have massive resources at their disposal whereas we are a small family business and we have limited resources at our disposal.

"We're continuing to hold to the stand that we took originally because we believe it's biblical, we believe it's what God would want us to do, and we also think that if we do cave in to the Equality Commission at this point it'll put pressure on other citizens who are defending their view of traditional marriage."

He added: "We don't want to be forced to promote a cause which is against our biblical beliefs. We've had a lot of support from people who disagree with our stance on same-sex marriage. They think that we should have the freedom to decline an order that conflicts with our conscience."

Simon Calvert, spokesman for The Christian Institute, said: "It is simply baffling for a body supposedly working for equality to be threatening a Christian family, all because of a cake.

"The Equality Commission has taken four months to dream up new grounds on which to pursue the McArthur family, claiming that they've breached political discrimination laws.

"Is the Commission seriously saying that all business owners have to be willing to promote every political cause or campaign, no matter how much they disagree with it? Does a printer have no right to refuse to print posters for the BNP or Islamic State?

"The Commission is throwing the kitchen sink at this case, and is wasting tens of thousands of pounds of taxpayers' money in the process.

"I doubt that many people in Northern Ireland will think this is a good use of their hard-earned tax money. I hope they will make their views known to the Commission."