I find "it's just business" and "it's not personal" to be some of the most insulting and gaslighting phrases in the English language, by how they dehumanize the person at the receiving end of them.
People are affected by loss of income, and it is tragic. I don't think a buyer ceasing to buy from a seller is injustice, regardless if the relationship is employer/employee or customer/business.
It is society that should be providing the stability necessary for business to just be business. If a business makes a mistake, it is not unjust for the business to correct course which could involve changing its terms with its vendors (including employees).
In regards to when an employee or employer can terminate buying or selling labor, US law outside of Montana is “at-will”, meaning either party can stop buying or selling labor anytime they want, barring a contract that stipulates otherwise.