The short answer is that you should not do it, but if you do it, you will probably be fine.  The reasoning is that a B-2 is a tourist-type visa.   It is for people who want to come and visit the US as a tourist or to visit friends or family.   It is not for people who are coming with some sort of purpose that could be viewed as business or religious.   There is a visa for people who want to come for a religious purpose — it is the B-1.

If at the consulate or at the border you say that you want to enter the US to be a m-ssionary, they will probably tell you that you cannot enter on a B-2.    However, things are never completely clear-cut at the border.   Perhaps you say that you want to come to the US to visit your friends and volunteer with their religious organization.   Perhaps, if the border guard focuses on the visiting your friends part of the description, he will let you in.   Perhaps if he will be okay with the idea that you are just coming to volunteer at a m-ssionary organization, even though he really should not.

The other option, which I think happens a lot, is that people say that they are coming to visit friends or to visit America.   That is true.   However, those friends are m-ssionaries with an organization here in the US, and the visitors are planning on volunteering at the m-ssion organization.  In my opinion, this is not really proper, and, if the border guard would know about it, he really should not allow it.    But, as I said above, the border guard might have allowed it anyway.   And, as long as there is no income for the visitor, most likely no one is going to complain about it or give the visitor a problem.   But, there is no guarantee.  You need to understand that there is somewhat of a risk to doing this, even though it is a small risk.  I think many, many people do this on a regular basis and never run into a problem — but I cannot recommend this because it really is not in line with what the B-2 visitor/tourist visa is intended for.

I hope this is interesting and helpful.   Remember that this is not legal advice.  It is just a summary of certain aspects of immigration law which may or may not apply to your situation.   I encourage you to consulate an attorney if you think any of this may apply to your situation.

Gunnar Armstrong