Sarah Mbuyi was dismissed for gross misconduct by nursery directors at Newpark Childcare in Shepherd's Bush, west London, after speaking to a lesbian colleague.
Miss Mbuyi claims that in January 2014 the colleague told her she was unhappy with the fact the Church was against gay marriage.
It's alleged the woman also said that God condoned homosexuality.
Miss Mbuyi told Christian Concern: "When I said 'No, God does not condone the practice of homosexuality, but does love you and says you should come to him as you are', she became emotional and went off to report me to my manager."
During an internal disciplinary hearing, Miss Mbuyi was confronted with the allegations and later dismissed for breaching the equality policy of the nursery.
She claims the hearing was "hopelessly one-sided" and is now hoping to use EU law to claim unfair dismissal.
The nursery worker will tell the tribunal that employees have the right to enter into conversations with adult co-employees subject to the normal principles of engagement in speech.
"It is obvious that we live in a climate where being Christ-like-following the Bible as much as we can-and being open and honest about that, is a problem now," she said.
In a statement, Newpark Childcare Shepherd's Bush said: "We are defending Ms Mbuyi's claim. We dismissed Ms Mbuyi for gross misconduct after she harassed a colleague on the basis of that colleague's sexual orientation.
"We have policies and rules in place, and a responsibility to our staff, client parents and their children to ensure a good working environment in which everyone is protected from suffering harassment or discrimination.
"Ms Mbuyi therefore made it untenable for her to continue working for us and we followed all the correct procedures when reaching and informing her of the decision.
"Ms Mbuyi was not discriminated on the grounds of her religion, her religious beliefs or for expressing a religious view.
"We employ a number of people who have different religious beliefs and we make allowances for them to practice their religion as much as we can. We are therefore defending the claim and we are confident in our position."