The gay couple who were barred from a Christian-run bed and breakfast in March have decided to sue the owners.
Michael Black, 62, and John Morgan, 56, will take legal action against Susanne and Mike Wilkinson, owners of the Swiss B&B in Berkshire.
They are being supported by human rights and civil freedom charity Liberty, which compared them to black American civil rights heroine Rosa Parks.
The couple had already booked a room and paid a deposit when they arrived at the B&B but Mrs Wilkinson turned them away when she realised they were two men.
She said that allowing them to stay would violate her religious beliefs.
Mr Black and Mr Morgan called the police over her refusal and were told they could make a civil claim against the Wilkinsons.
The Equality Act 2006 makes it illegal to refuse people goods and services on the grounds of sexual orientation.
James Welch, legal director of Liberty, said: “This case is as important to the principle of non-discrimination as Rosa Parks’ refusal to go to the back of the bus. A business with a ‘no gays policy’ is as bad as one that says ‘no blacks; no Irish’.
“Liberty defends the rights of religious groups to preach their beliefs, even when we disagree with them, but not to discriminate in the provision of goods and services.”
Mr Wilkinson said he was disappointed that Liberty was taking the side of the gay couple.
He told BBC News: “We are rather surprised that Liberty would be so one-sided in a matter of liberty because there are two liberties to uphold in this case.
“There is a religious liberty to uphold and there is the right for homosexuals to practise what they want to do. We have received the letter from them.
“We don’t want to go to court but if they want us to then I suppose we will have to. We are sorry we have offended these guys.”
The charity has defended religious rights in the past, such as cases of workers barred from wearing cross necklaces at work. However, it supported Islington Council in its battle against Lillian Ladele, the registrar who refused to carry out civil partnerships.
The B&B story became an election issue when shadow home secretary Chris Grayling was secretly recorded telling a meeting that he thought B&B owners should have the right to turn people away on the basis of sexuality but hotels should not.
He later said that people should be “sensitive” to faith groups but said he was satisfied with the current laws, which he voted for.