Mr McGrath is pressing for a common stance across all local authorities following the judgment of an employment tribunal in March that Glasgow had breached the law in barring a non-Catholic teacher from applying for the post of acting principal teacher of pastoral care. The city is currently appealing.
Glasgow, along with more than half of the other authorities, believed it was implementing the Church's right of approving teachers to work in the denominational sector by reserving some posts for Catholics only.
The Church had warned the city was breaking employment law and Mr McGrath said it had not been called to give evidence. The director emphasised that the judgment had not challenged the Church's right to approve teachers under the 1980 Education Act.
"Currently some councils have maintained a kind of selection system where they only look to the approval system for certain posts," he told The TES Scotland. "We would like there to be clear guidelines drawn up between councils and the Church that are fair to teachers, compliant with the law and ensure teachers approved to work in Catholic schools understand what their role is and understand there is a different set of expectations."
Mr McGrath said that some councils interpreted the test of "religious belief and character" to mean a policy of Catholics only for some posts, "but that is not what the Church is saying".
In primaries, for example, all teachers taught religious education. What the Church required was a qualification in RE, not a Catholics-only rule.