Vatican: A gathering of world Catholic bishops has been thrown into confusion with the leak of a letter from conservative cardinals to Pope Francis bitterly complaining that the meeting is stacked against them.

Australian cardinal George Pell gave the Pope the letter accusing him of stacking the cards against conservatives in an ongoing battle over issues including the church's approach to gays and to divorced and remarried Catholics.

Delivered letter: Australian cardinal George Pell. Credit:James Alcock

L'Espresso newsweekly, which published the English-language letter in full, said 13 cardinals signed the letter and one of them delivered it by hand to the Pope last week.

It was published by the same Italian journalist whose press credentials were stripped by the Holy See last June after he ran a leaked copy of the Pope's major encyclical on the environment.