A religious organization (by itself or in conjunction with another organization) can sponsor you as a religious worker if it is employing you in a position as a minister, a religious occupation, or a religious vocation for at least 20 hours per week. The regulations do list what is not a religious occupation but does not define what it is; therefore, carefully explaining the job duties and title are very important in these applications. A religious vocation is when an individual has made a formal lifetime commitment—through vows, investitures, ceremonies, or similar indicia—to a religious way of life. For example, nuns, monks, brothers, sisters, pastors, ministers, etc.
You must have been a member of the religious denomination or organization for the immediately preceding two years. This classification does not require prior employment with the organization though. Only Special Immigrant Religious Worker classification (green card) require prior employment. The membership requirement requires membership in the denomination—not the specific petitioning organization.