Heads of the Church of Ireland, Methodist Church in Ireland, Catholic Church, Presbyterian Church and the Irish Council of Churches are calling on members and congregations to pray, call for change, and to lobby their locally elected representatives.
Unless devolution at Stormont is revived within weeks, the Government is bound to liberalise the law surrounding terminations following the passage of Westminster legislation.
The church leaders said: "There is no evidence that these changes reflect the will of the people affected by them, as they were not consulted.
"They go far beyond the 'hard cases' some have been talking about."
They said they were gravely concerned that the imposition of Westminster legislation:
- Removes from law all explicit protection for the unborn child up to 28 weeks of pregnancy;
- Offers no specific protection for unborn babies with disability;
- Does not prohibit abortion based on the sex of the baby;
- Creates a potential vacuum of up to five months in Northern Ireland for unregulated abortion to exist with all the attendant health risks to women.
They invited their members to sign an online petition created by Baroness Nuala O'Loan, and added: "Our Northern Ireland political parties have it in their own hands to do something about this.
"They all need to take risks and make the compromises necessary to find an accommodation that will restore the devolved institutions.
"We are calling on the Secretary of State to recall the Assembly before 21 October to provide an opportunity for the parties to take the necessary steps both to prevent these laws coming onto effect and to find a better Northern Ireland solution for these challenging issues.
"Finally, we hope to meet with the Secretary of State to discuss with him our concerns, concerns that we share with a significant number of our fellow citizens of all faiths and none."
In July, MPs passed the Northern Ireland (Executive Formation) Act.
It placed a duty on the Government to regulate to provide for access to abortion in Northern Ireland.
It comes into effect if the Stormont executive is not restored by October 21, with regulations required to be in place by the end of March 2020.
Grainne Teggart, Amnesty International's Northern Ireland campaign manager, said: "Decriminalisation, which will take effect on October 22, does not equate to deregulation, it simply means that women will no longer be treated as criminals for accessing healthcare.
"Amnesty's Northern Ireland Office will issue interim guidance in advance of 21 October. The churches do not reflect the vast majority of the Northern Ireland public who we know have long favoured change.
"Finally, we are getting to a place where we will have a compassionate response to crisis pregnancy. The UK Parliament has legislated to make abortion lawful including in circumstances of risk to health, serious and fatal foetal abnormalities and in cases of sexual crime - few disagree it should be available in these circumstances.
"There must be no return to Stormont without abortion reform agreed on exactly the same terms as has been secured at Westminster.
"These rights have been long and hard fought for and we will not accept these being sacrificed for political expediency. It would be foolhardy of any political party to think otherwise."
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