Falkirk Council is proposing that pupils who are not Catholic will have to put in a placing request to enter the schools, even if they live inside the catchment area.
As in the rest of the UK, such schools have a mixed roll including pupils of different faiths or none but councils are legally obliged to provide denominational education to Catholic pupils.
A Falkirk council report said almost 40 pupils were denied enrolment at Catholic schools last year, lengthening the waiting list for places.
It said: “It was not possible to reserve any places for pupils likely to move into the area because the demand came from pupils that live in the catchment areas of these schools.
“As a consequence, there are no places available in primary one at several denominational primary schools for Catholic pupils that move into the area, and this has resulted in a growing waiting list for places.”
It is understood the plan would apply to secondary as well as primary schools.
Significant investment has been put into the school estate in recent years to raise capacity, the council said, but demand has still grown beyond this.
It concluded: “We are proposing that the schools admissions policy is changed so that Roman Catholic-baptised pupils will still be entitled to enrol at their catchment denominational school, but all other pupils would have to submit a placing request. This would mean spaces could be reserved for Catholic pupils where necessary.”
The Scottish Secular Society has urged Falkirk council not to “discriminate” against children wanting to attend Catholic schools from other faiths or no faith.
A spokesman said: “The council is planning to introduce a discriminatory schools admission policy to ensure children who are baptised into the Catholic Church are given priority over other children getting into these schools.
“Catholic children will need to show a baptismal certificate to prove they are Catholic and any unfilled places will go to children of parents of other religions and none.”
Michael McGrath, director of the Scottish Catholic Education Service, said there was no national policy on the issue but councils had put similar strategies in place to ensure first right of access for Catholic pupils in rare cases where popular schools were oversubscribed.
If councillors back the plan after consultation, the policy will be implemented from December.