A Christian bakery owner who refused to make a cake with a slogan supporting gay marriage says he has been threatened with legal action unless he pays compensation.

Family-run Ashers Baking Company in Northern Ireland earlier this year declined the order for a cake with the image of Sesame Street puppets Bert and Ernie below the motto Support Gay Marriage.

In the wake of its refusal to provide the service, the Equality Commission for Northern Ireland, a state-funded watchdog body set up to ensure compliance with anti-discrimination laws, took on the case on behalf of the customer, a gay rights activist.

General manager of the bakers Daniel McArthur said he had now received a letter from the commission claiming his stance breached legislation.

He said the letter told the company if it did not offer compensation within seven days it would face litigation.

Mr McArthur said his family would not be forced to promote a cause that 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.

"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."

Gay marriage is a highly divisive issue in Northern Ireland and while the bakery's decision was backed by Christian advocacy groups it faced criticism from gay rights organisations arguing that discrimination in delivering services was illegal.

The devolved assembly at Stormont has rejected several attempts to change the law on gay marriage and local politicians have intervened on both sides of the bakery debate.

Simon Calvert, spokesman for the Christian Institute, which is supporting the McArthur family, said: "It is simply baffling for a body supposedly working for equality to be threatening a Christian family with legal action, 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.

"If supporting same-sex marriage is a protected political opinion, so is supporting traditional marriage. Yet the Commission clearly favours one view over another and is prepared to litigate to prove it.

"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."

Ashers was founded in Newtownabbey, north of Belfast, in 1992.

The Christian directors oversee six shops in Northern Ireland and employ around 60 people.

The company was named after a verse from the Bible, which refers to "Bread from Asher".

A spokesman for the Equality Commission confirmed a letter had been sent to the bakery.

The spokesman for the Equality Commission said: "The Commission confirms that it has written to the solicitors acting for Ashers Baking Company responding to the points made in their earlier letter on behalf of the company and its directors; and setting out the grounds on which unlawful discrimination is alleged.

"In its letter the Commission stated that they would prefer not to have to litigate these issues and sought an acknowledgement that there has been an unlawful breach of the equality laws and an assurance that this will not be repeated.

"It made clear that the claimant will be seeking only modest damages for the upset and inconvenience caused and that, failing this, a civil bill will be issued.

"The Commission has now received a response from the company's solicitors stating that their view remains unchanged that their clients have not acted unlawfully, confirming they have no further proposals to make on their clients behalf and that they will accept service of a civil bill in regard to this matter.

"The Equality Commission has an important role in ensuring effective application of Northern Ireland's equality laws and supports cases so that people are aware of, and can avail of, the protection these laws afford against all forms of unlawful discrimination.

"This 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.

"The Commission will be issuing a civil bill in this case and a decision as to whether or not discrimination has occurred will be a matter for the court. The Commission will not be making further comment on the facts or issues in the case before a court hearing."