Many leadership roles in the organized church have been restricted to males. In the Roman Catholic and Eastern Orthodox churches, only men may serve as priests or deacons, and in senior leadership positions such as pope, patriarch, and bishop. Women may serve as abbesses. Most mainstream Protestant denominations are beginning to relax their longstanding constraints on ordaining women to be ministers, though some large groups are tightening their constraints in reaction. Charismatic and Pentecostal churches have embraced the ordination of women since their founding.