What are some disadvantages of a visiting union?

Much more information is needed on your question, in order to receive any meaningful replies.

Can you define a "visting union" over union membership ?

What type of industry, since unions have more or less advantages by the industry.

And at least in the US, which union, some are more effective than others.

** of course if I assume this is a home work question, then it is the answer in your text that the teacher wants. Not a real life specific answer