A group of Roman Catholic cardinals including the influential Archbishop of New York, Timothy Dolan, have written to Pope Francis warning him that the Synod on the Family meeting in Rome is in serious trouble and is being manipulated in favour of liberals.

The story was broken by Sandro Magister, a veteran reporter who was banned from the Vatican for leaking a copy of the Pope's Laudato Si' encyclical on the environment.

The synod is considering incendiary questions such as whether divorced and remarried Catholics should be able to receive communion, how the Church should treat gay and lesbian members and what it should do with couples who live together without being married.

Conservative participants have been deeply worried that the Church's traditional stance on moral questions will be undermined in the final text of the synod's concluding report.

According to Magister, the document says that the synod process seems designed to "facilitate predetermined results on important disputed questions".

The bishops complained in the letter that new synod procedures lack "openness and genuine collegiality" and that "a vital pastoral matter" – the importance of marriage and family – could be overshadowed by the question of Communion for divorced Catholics. They also complain that members of the drafting committee were appointed by Francis rather than elected by the bishops.

The letter is at its strongest when it refers to the numerical implosion of denominations such as the Episcopal Church in the US, saying: "The collapse of liberal Protestant churches in the modern era, accelerated by their abandonment of key elements of Christian belief and practice in the name of pastoral adaptation, warrants great caution in our own synodal discussions."

Pope Francis said at the beginning of the synod that participants should not give in to what he called "the hermeneutic of conspiracy" which he said was "sociologically weak and spiritually unhelpful". He asked them instead to engage in "a profound discernment to seek to understand what the Lord wants of his Church". His unscripted intervention is now being seen as a response to the letter.

The list of signatories to the letter includes some, including Archbishop Dolan, who would not normally be seen as arch-conservatives.

However some, including Péter Erdö, Archbishop of Esztergom-Budapest and president of the Council of the Bishops' Conferences of Europe, have since distanced themselves from the letter, saying that they had not signed it.

The letter reflects what appears to be unhappiness at a process that signatories fear is rushing them towards changes in Catholic practice that might be ill thought out and would be irrevocable. Some commentators have warned that the synod might split the Church and questioned the need for it in the first place.