Christian Solidarity Worldwide is seeking legal advice after a row broke out with donation website The Big Give during a £1m match-funding giveaway, funded by the Reed Foundation.
CSW claimed each charity should have been eligible for up to £20,000 to match other donations, but that these terms were changed during the event. The Big Give denied the terms were altered.
Corinna Loges, director of communications at CSW, said The Big Give had decided halfway through the event to group it with other Christian organisations, meaning they were only eligible for £20,000 match-funding between them.
The non-religious Reed Foundation, which set up The Big Give, did not want most of the £1m to go to charities promoting Christian faith, said Loges.
Jon Brooks, director of The Big Give, said CSW had agreed to the terms by taking part. "These include: 'the Reed Foundation reserves the right to cease or limit the matched funding delivered to any charity or sector and to terminate the matched donations at any time'," he said.