The GTCW is urging independent school heads to only employ registered teachers.
Currently while state schools in Wales can only employ teachers if they are registered with the GTCW, independent schools are free to employ unregistered teachers.
And according to the professional standards body only 20 per cent of teachers in the independent sector are registered.
The appeal comes after the Welsh government failed to include teachers in independent schools among new categories of staff who must be registered by law under new legislation.
GTCW chief executive, Gary Brace said: “By embracing registration and regulation an independent school will be signifying to parents that its teachers adhere to the highest standards of professional conduct and competence and conform to a rigorous code of practice.
“Parents will be further reassured by the fact that registered teachers have undergone enhanced DBS (previously CRB) checks to ensure they are suitable to teach and have undergone proper refresher training if they have returned to teaching after an absence of more than five years,” he added.
Under current regulations, a teacher who is struck off the register for professional misconduct or incompetence is banned by law from teaching in any state school.
However the ban does not cover independent schools so a prohibited teacher would still be free to seek a job in that sector.
Teachers who are dismissed from their jobs in the state sector in Wales are automatically referred to the GTCW for investigation and possible removal or suspension from the register, whereas no such referral is required if an unregistered teacher is dismissed from an independent school.
Mr Brace added: “Teachers dismissed from schools in one sector should not be treated any differently from those in another sector.
“It is safer for the public if there is a single register for all qualified teachers that can be checked by any prospective employer and that all cases of professional misconduct or incompetence are investigated and dealt with in the same way.”
Under new legislation, the Welsh government proposes to expand professional registration and regulation to cover teaching assistants, further education lecturers, work-based learning tutors and certain categories of youth workers.
Eventually all of these will need to be registered with a reconstituted GTCW.