Catholic bishops are warning ministers against a possible U-turn on a pledge to remove the 50 per cent cap on school places allocated on the basis of faith.
Current laws means all new faith schools must award half of its places to pupils irrespective of religion.
Campaigners in favour of the restriction say the cap prevents discrimination and means faith schools are more diverse. But the Catholic Education Service says because Catholic schools are heavily over-subscribed, it effectively means Catholic pupils are turned away precisely because they are Catholic in order to fit the quota.
For this reason, it says, no new Catholic schools have been opened since the cap came into force under the Tory-Lib Dem coalition government because it breaks the Church's Canon Law to refuse a Catholic pupil a school place because of their faith.
The 2017 Conservative manifesto, masterminded by Theresa May's former adviser Nick Timothy, vowed to remove the cap, saying the 'unfair and ineffective inclusivity rules prevent the establishment of new Roman Catholic schools'.
But the Education Secretary Justine Greening is understood to be considering a U-turn on that policy.
When approached by Christian Today the Department for Education said they would be making an announcement shortly.
Now Catholic bishops are launching a plea for Greening to rescind the cap, pointing out she has admitted it 'the rule has been ineffective and adversely affects Catholic families'.
A petition launched by the Catholic Bishops Conference of England and Wales reads: 'By forcing Catholic schools to turn away Catholic school children on the basis of their faith, the very principle of a Catholic parent's right to choose a Catholic education is under threat.'
It comes after the bishops, at their most recent meeting earlier this month, said education was crucial to their mission and vowed to 'continue to strive to provide a Catholic school place for every Catholic child in their respective dioceses'.
A resolution passed at the conference read: 'The principle of parental choice is fundamental to both Catholic education and the current educational policy in England and Wales, and for more than 150 years Catholic parents have had the opportunity to choose a Catholic education for their children.
'Therefore the Bishops' Conference welcomes the supportive comments made by the Prime Minister and the Secretary of State for Education about Catholic schools and their acknowledgement that the admissions cap is an issue which actively targets the Catholic community, as Catholic parents are the principle religious minority adversely affected by the admissions cap.
'We therefore call on the Government to honour its Manifesto commitment.'