When his boss is the owner, exactly how does one "throw his weight around" in this situation? Threaten to quit? 1) that's what I think they want him to do, and 2) that hurts my FIL a lot in the short term. My FIL doesn't have a lot of cards to play here, other than his experience.

I don't know about you, but I've seen a LOT of employers who make poor decisions based upon a short-term perceived gain. Maybe the employer got himself in some trouble, and is trying to quickly save some cash? Firing the long-term old guy seems like a pretty easy thing to do.

Maybe one or more of their major clients is dropping them, and that's the project my FIL is working on, but the employer doesn't want to pay a severance package? This actually makes a lot of sense, now that I think about it. I would bet the contractually have to pay a severance package with a layoff, but if the guy quits or is fired they don't have to.