The Catholic Education Service said the move, which contravenes the Government's new draft admissions code, could discriminate against some pupils.
Oona Stannard, its chief executive, said it was "undesirable", and admissions rules should be "as transparent, straightforward and undaunting for applicants and their families as possible, whatever their background".
She spoke out after Ruth Kelly, the Education Secretary, ruled that the London Oratory school - where the Prime Minister sent three of children - could continue to interview. Ms Kelly admitted that interviewing can "lead to schools cherry-picking articulate applicants and their families at the expense of less articulate, but equally worthy, applicants".
The Education Secretary also said that interviews can have a "potentially intimidating effect" on pupils, deterring families from applying to certain schools.
But she said interviews by the London Oratory, which draws pupils from more than 400 parishes and primary schools and 40 local authority areas, were justified given the size of the school's catchment area.
In a report, Ms Kelly said the Department for Education and Skills had identified three other London schools - Douay Martyrs, in Uxbridge, and St Joseph's college and St Mary's high, both in Croydon - which also interview pupils when they are oversubscribed. In a further twist, the Education Secretary said a fifth Catholic secondary, Gunnersbury school in Hounslow, should stop interviewing because its admissions policies lacked clarity.
She said it was possible for the school to gauge religious commitment by other means, such as a letter. Schools are expected to follow the code on admissions but may deviate from it in exceptional circumstances, leading to Ms Kelly's judgement's on the London Oratory.
Chris Waterman, executive director of Confed, which represents senior education officers, said: "It is a joke. Schools only need to 'have regard'
to the present admissions code and it is clear that too many are flouting it and getting away with it.
"Interviews simply allow the more ambitious parents to work the system to get their child into a particular school."
But Eamon Connolly, head of St Joseph's, which offers parents the choice of an interview, but does not quiz the pupils themselves, said: "It is quite daunting for parents to fill out a form. It is often the most articulate who can produce a beautifully presented and well-typed application. It is much more transparent to allow parents to talk to the headteacher face to face."