You’ve actually raised two very interesting job-related questions. The first is the divide between ministerial and non-ministerial employees. The second is the divide between professionals and hourly workers.
Religious organizations have a lot of freedom to choose their ministers, because the work of the ministers actually defines the organization’s position and activity. They can impose religious standards, character standards, behavioral standards, and so on. It’s called the “ministerial exception” because Title VII specifically does not apply to them. Constitutionally, various other employment statutes probably cannot apply to ministers either. Many missionaries, perhaps even most missionaries, fall into the ministerial exception. However, certain personnel, such as missions staff and administrative people, might not fall into the exception, depending on their job description and role. It is worth taking a little time and effort to draft job descriptions for different positions and determining whether the position is considered ministerial or not. (There can also be tax and benefit implications, which are beyond the scope of this blog.)
If an employee of a mission does not fit the ministerial exception, there is still freedom under Title VII to discriminate in hiring according to religion, which means the mission can require certain beliefs and behavioral standards. But it’s not as generous a protection as the ministerial exception.
The next big divide is whether a person is paid hourly, and is entitled to time-and-a-half if he or she works overtime. This is the staff v. professional divide. (There are other categories of worker that don’t get paid overtime, such as computer programmers and sales people, but for simplicity, we won’t consider those.) If someone is pure staff, you had better be thinking through those evening calls and emails, as the person may be entitled to overtime pay for it.
Most missionaries are going to be professionals—in fact, the variety of professional known as clergy! As any young law firm associate will tell you sadly, overtime does not apply to professionals. Professionals can work as much as they want to or have to. As a psychologist, if you handle a patient emergency in the middle of the night, you don’t go on time-and-a-half. As a pastor, someone showing up with an emergency or personal need one evening is part of your job. I often check client emails from the U.K. as I roll out of bed in the morning and respond to questions from the Far East at 10:00 p.m. That’s just part of being a professional.
Professionals are assumed to love their job and be willing to do whatever is necessary to get the job done (you see, being an attorney is like being a mom). I think most of us who serve or have served as missionaries would agree with that! So the answer to your question is that it’s okay for the job description to be fluid.
Disclaimer: not official legal or psychological advice or opinion