The National Association of Teachers of Religious Education (NATRE) revealed the figure after carrying out a survey of 625 schools - 53 of them Catholic.
The study found that 33 per cent of responding schools were not meeting their "legal requirements" under the terms of their syllabus agreements at Key Stage 4 (14-16 year olds).
The survey found that at least eight Catholic schools did not meet the legal requirement at Key Stage 3 (11-14 year olds) and 11 schools said there had been a decrease in specialist RE staff.
State schools are required by law to teach RE to all pupils unless parents choose to withdraw them from lessons.