In the US, employment is generally at-will, which means either side can unilaterally terminate the agreement but either way, these are the people whose employme

In the US, employment is generally at-will, which means either side can unilaterally terminate the agreement but either way, these are the people whose employment conditions presently include having to physically show up to work. So, there's no "existing employment contract" here either legally or morally - if want to change one side of the contract (from working in the office to working from home), then it's reasonable for the other side of the contract (compensation) to have to be renegotiated.