An atheist rights campaigner is threatening to take the BBC to court if it does not lift its ban on non-believers contributing to Radio 4's Thought for the Day.
The former President of the National Secular Society has had lawyers write to the corporation's Board of Governors telling them their ban is a breach of her human rights.
The instructions by Barbara Smoker follows legal advice from a barrister in the human rights chambers Matrix.
Ms Smoker said: "Around 30% of the population of this country does not hold to any religion, and yet this large minority is denied voice on Thought for the Day.
"It is inconceivable that none of these people has any relevant thoughts on the ethical and moral issues of the day."
More than 100 people sent a letter to the BBC earlier this year demanding the ban be lifted but the BBC insisted the three minute daily slot, broadcast in an interval in the Today programme, would remain exclusively for religious contributors.
A spokeswoman for the BBC said: "The Thought for the Day is a slot where people can reflect on current affairs from a religious and faith based perspective and as such it would be inappropriate for an atheist to contribute."
She said the BBC had received a letter from Ms Smoker and were dealing with it in the usual way but that it had not received legal action.
Ms Smoker, who has been involved in fighting the ban on atheists for more than 30 years, added: "Minority religions representing just 1% of the population secure frequent slots on this programme."
She added that the BBC has 14 days to justify its position before lawyers seek a judicial review of this decision.