Collaboration difficulties that are of a serious nature may constitute valid grounds for termination. However, general unpleasant behavior or two individuals not getting along are not sufficient for termination.
The crucial factor is how essential the ability to collaborate is for the specific work. For a supervisor, the ability to collaborate is crucial, but for someone working independently, it may be less important. As an employer, one must investigate the problem, for example, the employer can relocate one of the individuals involved. Other measures may also be applicable.
The extent of your obligations as an employer is determined by the size of the company.
In other words, it is difficult to point out a general rule, as there are many factors beyond collaboration itself that affect the situation.