Led by the Bishop of Coventry, the Rt Revd Christopher Cocksworth, the call is also backed by the Roman Catholic Church's foreign affairs spokesman, the Rt Revd Declan Lang, the Bishop of Clifton, leader of the Coptic Church in the UK, Bishop Angaelos, and the Greek Orthodox leader Archbishop Gregorios.
The Bishop of Bedford Rt Revd Richard Atkinson has signed the letter.
He told Premier: "The letter asks that we do work through the United Nations.
"We've obviously got to be cautious of how we tread.
"I think at the moment the combination of military support and of advice.
"But as always I really do believe it's about the nations of the world working together."
It comes as violence by I.S., formerly ISIS, continues to grow in Iraq.
Yesterday a Catholic American journalist was beheaded before a video of his death was posted online.
Tens of thousands of Christians have been forced to flee as I.S. gives them an ultimatum to convert to Islam, pay a tax or be killed.
The letter, published in the Daily Telegraph, wants assurances from the British Government that the militants will be held responsible for the "gross and systemic" killings of religious minorities.
It said: "Such violations as are currently taking place are crimes against humanity that must be both stopped and punished.
"The culture of impunity within which these dehumanising atrocities have been committed needs to be challenged most vigorously.
"Given that Iraq is not a state party to the International Criminal Court, the Government must now work towards a United Nations Security Council Resolution that refers this matter to the International Criminal Court for investigation and where necessary prosecution.
"The international community must send a clear signal of intent to those who are committing such atrocities that at some point they will be held accountable for their actions."
The letter is also backed by Muslim, Jewish, Hindu, Sikh and Zoroastrian leaders.
It continued: "Governments, international institutions and Non Governmental Organisations need to recognise this wider crisis and commit the necessary time, energy and resources to ensure greater respect for this fundamental freedom in order to attempt to forestall such further tragedies."
Listen to the Bishop of Bedford Rt Revd Richard Atkinson tell Premier why he signed the letter: