The Archbishop of Canterbury delivers Thought For The Day on Good Fridays
The BBC Trust has rejected complaints about a ban on non-religious contributors to the Thought For The Day slot on Radio 4's Today programme.
Allowing only religious content did not breach BBC guidelines on impartiality or its duty to reflect religious and other beliefs, its governing body said.
The National Secular Society said the decision was "a rebuke" to people who did not have religious beliefs.
The British Humanist Association said the policy was an "ongoing injustice".
The trust was responding to 11 appeals following complaints about the slot as well as a further appeal about the BBC's policy on non-religious programming.
Complainants said the BBC's stance on Thought For The Day was discriminatory against non-religious groups and contributors.
Richard Tait, chairman of the BBC Trust's editorial standards committee, said: "We understand that some people feel strongly about this issue and have given it careful consideration.
"However, we have concluded that the current arrangements do not breach BBC editorial guidelines and specifically requirements of due impartiality in content."
A Church of England spokesman said Thought For The Day was "a unique slot in Radio 4's schedule where religious views from across the faith communities of the UK can be expressed openly".
"Thought For The Day is highly valued by people of all faiths, and none, as a distinctive slot that, if diluted, would have become nothing more than just another comment slot."
The National Secular Society's president Terry Sanderson said the policy sent the message to people without religious beliefs that "their thoughts are not worth hearing and that somehow religious opinions are more worthy of a special, unchallengeable platform".
"This is so blatant an abuse of religious privilege that we cannot simply let it pass," he said.
"We will be looking at other ways of challenging this unjustifiable slot."
And Andrew Copson, of the British Humanist Association, said: "This is a real missed opportunity to correct the ongoing injustice of the exclusion of non-religious speakers on the programme.
"We can see no good reason whatever why humanists are barred from making their contribution."