Regardless of its commonality, and exclusivity clause in a part-time contract would be *very* unreasonable, and I would question the bona fides of an employer who proposed it.

Without seeing it, it's hard to know exactly what you mean by an "exclusivity" clause, but I wouldn't assume the employer even knows exactly what it's asking for -- or its impact -- since many contracts these days are built on templates taken from the internet.

Typically, an exclusivity clause is used to protect an employer's legitimate business interests (especially those involving of a special proprietary nature) from potential competitors. I'd find it hard to understand what "competition" an average parish is trying to protect itself from.

If the employer confirms that the inclusion of the clause is intentional, though, I'd start with trying to get the employer to describe its true interests (vice mere "position", i.e. that an exclusivity clause is required, period).

Does the employer fear that other employment will somehow bring scandal or discredit to its own enterprise? Is the employer concerned that other employment will be given priority over its own needs?

There are other, better terms/conditions to address these issues rather than to demand an exclusivity clause. Or, as in other business settings, to offer some premium in return for exclusivity.

I have never heard of this in church music. Perhaps if you work for another church at a better wage, it could show your original employer is a cheapskate. Other than that, what would be a valid reason for it?

Agreed, weird. Now I want to know the wording, but also if this is a real, actual situation, or just a potential one.

I was helping a friend who was negotiating a contract recently and there was a line in there that didn't allow him to play/substitute at other churches. I advised him/her to ask them to remove it, he/she did, and they agreed.

In business, this would be a way to keep sensitive information from flowing to the competition. So in a church context, let's imagine that a contract would exclude you from working at another Christian church across the street - or even a non-Christian church of some sort.

I can't imagine what that would accomplish. Some kind of weird "we don't want you to lose your soul to another religion" thing? Or is it a subtext of "we want to make sure we extract as much time out of you as possible"?

Like everyone's saying: Weird. And out of context.

All of our parish employees received an employee handbook at our last full-staff meeting. There was a clause that said any other employment was not "forbidden" but it could not affect job performance at the church.

I think most paid parish musicians and DMs probably either need to (living wage) or at least enjoy pursuing other musical endeavors. Like Mark said, other opportunities, can help boost, directly or indirectly, a parish music program.