A care service manager resigned in protest at "Christian-only" policies allegedly in place at the charity he worked for, a tribunal has heard.
A humanist group is supporting Mark Sheridan's claims
Mark Sheridan, 56, is claiming discrimination and constructive dismissal against Prospects, for whom he worked in Conwy.
The hearing had been told the charity had changed its recruitment policy to hire only practising Christians.
But the organisation, whose head office is in Berkshire, denies discrimination.
Prospects offers Christian support to people with learning disabilities.
Mr Sheridan, who worked for the charity in Conwy for eight years, told the employment tribunal that workers were expected to promote the Christian ethos.
He resigned twice in four months, withdrawing his resignation the first time before finally resigning in January last year.
But the tribunal in Conwy heard he did not mention his reasons for leaving in his resignation letter.
Asked why he did not mention his discomfort at the new rules, Mr Sheridan said: "Although I felt uncomfortable with it, I didn't feel in my heart this was a good approach, I was being told that there was no other option and I suppose I did trust and have confidence in my managers."
When asked why he had withdrawn his first resignation, he said: "I was in turmoil over what was happening in the service.
"The consequences were causing difficulties for me as a manager and me as a person.
"I was struggling because I knew the morale of the service, not just non-Christians but Christians too, was not great."
He also said that he struggled to maintain staffing levels because of the charity's policy.
Mr Sheridan said the charity had an evangelical arm called Causeway Prospects which promoted "Christianity with regard to people with learning disabilities" but he said he was not a part of this and he was not expected to evangelise.
He said: "We worked within a Christian ethos and respected people's wishes to either choose or not choose to ask for spiritual support.
"If people asked questions, we responded. To actively promote Christian belief to people who have expressed no particular interest, was not part of the remit as I saw it."
Mr Sheridan, who describes himself as a former Christian, is being supported by the British Humanist Association (BHA).
A spokeswoman said: "This is a potentially landmark case because of the extent to which religious organisations are able to attach 'genuine occupational requirements' to their jobs has not so far been tested."
Care worker Louise Hender, who also worked for the charity, claims she was denied promotion on the grounds of her non-religious beliefs.
She is expected to give evidence on Wednesday.