Universities are making it tougher for adults who do not have University Entrance to become students.
Students do not need UE if they are over 20 - they can enrol in university through special admission.
But the Union of Students Associations says universities are screening special-admission applicants more closely.
The change has been prompted by government caps on enrolments and rules that link funding to students' pass rates.
The University of Canterbury's vice-chancellor, Rod Carr, says the enrolment cap means universities need to give enrolment places to the students most likely to succeed.
He says students aged 20 to 25 who do not have UE have a pass rate of 50% in their first year.