I have a suspicion that what you mean is:
'Because "A" has cooperated with "B" for many years now, "A" allows free of charge access for workers organised by "B".'
You could replace "for" with "to", ie "free of charge access to...". It really depends on the nature of the access, so I cannot be certain which is better.
A context would likely make this more understandable, but I assume there is some kind of service "A" provides, and charges for, but is granting free access to the workers employed/organized by "B" in recognition of the long relationship between "A" and "B".
Interested in Language