Parents As First Educators president Teresa Pierre announced a petition on Monday and is urging Catholic school trustees to sign it.
Pierre says they're asking Catholics to demand the Ontario English Catholic Teachers' Association not officially attend the World Pride Parade.
Pierre says the event is inconsistent with what the church teaches about homosexuality.
She says Catholic parents expect a Catholic teachers' union to support the teachings of the church on marriage and family, adding that the parade breaks nudity laws and participants promote homosexual activity.
The union, which represents about 34,000 teachers, hasn't commented on the petition.