A company shouldn't be able to fire an employee over their opinion,[0] so that wouldn't matter to me. For a major owner, the donation amount starts to matter to me around $5-10K, but YMMV.
[0] I suppose unless they have a very influential position and it's about a matter that contradicts main company goals
What if the employee's opinion is that the employee should murder the CEO?
Oh, come on. If you're trying to make a point, be more clear.