Hi MadiMo,
I think this is a perfectly understandable question. Some companies will include things such as resources in their requirements and others will go a slightly different route, by adding it in a Business Case for example.
Neither are right or wrong. It just depends on what the company you work for does.
So, lets answer your question.
If we assume that a resource is a person or a thing (such as a specialist piece of equipment) then saying that you need one (or more) in order to do the job, could be construed as a non-functional requirement. You aren't asking it to actually do anything, you are just saying that to meet expected capacity you need x number of people (if we use the people resource example).
So if I were to add them into my requirements, it would be as a non-functional requirement.
If it is a piece of equipment, the same is still true. You haven't said in you requirement that it should 'Open an envelope' for example. So it still counts as a non-functional requirement.
The difficulty with this though, is that it is often easy for everyone to forget about this type of requirement. So, I would also make sure that the Project Manager, Sponsor and Product Owner (if you have any of those) are aware of this early on, and remind them of the requirement periodically. As the BA, you may be challenged later on to prove that this requirement was met - that wont be easy unless you can actually point to the new person, or piece of equipment.
I know your original question was around 4 months ago, but if you do read this, I would be interested to know what the Resource was in this case. Just me being nosey !!