David McNab, 53, a maths teacher at St Paul's High in the Pollok area of Glasgow, said he was aware the post of guidance teacher required Catholic accreditation, but he claimed that after the McCrone agreement, this post was replaced by the post of pastoral care teacher which also covered learning support.
Glasgow City Council argues that Catholic Church approval was a genuine occupational requirement for the post, and that pastoral care is essentially the same post as guidance. It denies discrimination on the grounds of religion or religious belief.
Mr McNab told the tribunal that the notice advertising the job did not mention Catholic accreditation and that Catholic Church approval was not required for his appointment as a maths teacher.
"As far as I was aware the law had changed in December 2003. It was illegal to discriminate in terms of religion for any job. I assumed that held for everyone and for every job," he said, in a reference to new UK legislation outlawing discrimination on the grounds of religion or religious belief.
The tribunal heard evidence that the Roman Catholic Church drew up a list of "reserved" posts which meant that all candidates had to be approved by the church before they could be appointed.
These included headteachers, depute and assistant heads, principal guidance and biology teachers, and all religious teachers at denominational schools in the West of Scotland.
Keir Bloomer, a former depute director of education in Strathclyde Regional Council and now chief executive of Clackmannanshire Council, said Catholic teachers had to satisfy the Catholic Church as to their "religious belief and character" in order to gain "approval" if they were seeking jobs at Roman Catholic schools.
However, rules requiring all teachers at demonational schools to be Catholic were relaxed in the 1960s because of a severe shortage of teachers, particularly in the Catholic sector, he said.
Mr Bloomer said: "The Catholic sector would really have struggled to survive, were it not for the fact that it recruited substantial numbers of non-Catholic teachers. By the late 1960s any Catholic secondary school would have had a significant proportion of non-Catholics for its teaching staff. But there were some posts, such as headteachers, principal teachers of biology and guidance and teachers of religious education where the Church did insist the only eligible applicants were Catholics."
Citing reasons the Church might give for non-approval of Catholic teachers, Mr Bloomer said: "Not sending their child to a Catholic school was quite a common one. I think that being divorced and remarried tended to be something the church regarded as a just cause for withdrawing approval."
George Gardner, deputy director of education with Glasgow City Council, told the tribunal that guidance teachers would be expected to follow the Catholic line when dealing with issues such as sexuality, pregnancy and contraception.
Asked by the tribunal if he felt it was morally correct that the only advice that could be given to a non-Catholic pupil at a Roman Catholic school who found herself pregnant was to have the child for doctrinal reasons without explaining the full range of options, Mr Gardner said: "It is the Roman Catholic principles and faith that determine how the school operates. I think the answer to that question is yes."
Mr Gardner said there were around 110 reserved posts in Glasgow's 11 denominational secondary schools for which the successful applicant had to be approved by the Roman Catholic church, and around 700 primary school posts.
The case continues.