“The chief justice must be applauded for upholding society’s most fundamental rights freedom of speech and freedom of religion,” the group’s director Errol Naidoo said in a statement.
He said there appeared to be prejudice against Christians in some media, which portrayed Mogoeng as a “religious nut intent on dragging the nation back to the Dark Ages”.
“The media’s attacks on Chief Justice Mogoeng exposes its anti-Christian bias,” he said.
On Wednesday, Mogoeng defended a speech he gave in Stellenbosch last week about religion’s role in law. He said religion could be used to strengthen legislation and lead to a better society.
“I take my oath of office very seriously and I made it clear I will not give precedence to my faith at the expense of the Constitution,” he told reporters in Johannesburg on Wednesday.
Mogoeng, who is a lay minister, has been criticised for his strong religious views.
Naidoo asked why a television news channel had interviewed a constitutional expert and gay rights activist on whether Mogoeng was fit for office in light of his religious beliefs.
The channel had, however, not consulted Christian legal experts when openly gay Judge Edwin Cameron was appointed to the Constitutional Court, Naidoo said.
On Wednesday, Mogoeng said he had promised to protect all citizens’ rights, including those of homosexuals.
“I know as a Christian that the Bible speaks against homosexuality, but I have taken an oath and I am very serious about my oath,” he said.
“My responsibility is to ensure that every gay person, every lesbian person enjoys their right as protected by the bill of rights. There’s no question about that.”
The Family Policy Institute describes itself as a “non-profit research and educational organisation dedicated to articulating and advancing a family-centered philosophy of public life”.