Churches go to the High Court in Belfast today to argue that the Sexual Orientation Regulations restrict their human rights.
If they are successful, the regulations that protect gay rights could be declared unlawful.
The case, which has been brought by The Christian Institute along with other Christian groups, is scheduled to last three days.
Colin Hart, Director of The Christian Institute, said: “I believe these regulations discriminate against Christians on the basis of their religious beliefs on sexual ethics.
“They were introduced under direct-rule powers by Peter Hain without proper consultation.
“We have the support of both sides of the religious community in Northern Ireland. People are particularly concerned about the regulations’ impact on schools.”
He added: “We hope our legal action will be successful and that these regulations will be declared unlawful.”
The sexual orientation regulations (SORs) prevent the LGBT community from being discriminated against by people who provide goods and services.
For example, it is now illegal in Northern Ireland for a doctor to turn away a gay patient, or for a hotel to refuse a bed to a same-sex couple.
If the regulations in Northern Ireland are found to be unlawful, it could have consequences for the similar British regulations.
A recent YouGov poll commissioned by Stonewall found that 85% of Britons support the 2007 Sexual Orientation Regulations.