Why is 'do not be unfair' not a precept? And some related questions on precepts What's the rationale or logic behind the precepts? 
Does fairness come into it? 
Are the list of precepts ever expanded to accommodate changing contexts?


Being very unfair to someone who trusts one is pretty similar in emotional harm to cheating on a spouse or lying, especially when the unfairness is made possible because of an abuse of a position of power. 

For example, employees of large corporations often feel lied to, even cheated when they are laid off by their employer because of new management policy. Yet, these are explicitly the terms of most employment contracts.

Similarly, a home owner can feel pretty awful when evicted by the bank or lender for failure to pay the mortgage, especially when the bank is usually writing all the rules ab-initio protecting itself from market risks. Yet, this too is an agreed upon constraint because one party operates from a position of power.

Modern life relies on governments, corporations and other faceless institutions to a large degree, and they do wield a great deal of power, so a lot of their transgressions fall afoul of the fairness test, though technically none of them are lies. This has to be a large source of misery in this world today.

Yet, going by the precepts, at least to me, such behaviour doesn't seem to be overtly criticised.

Does Buddhism have anything to say to such scenarios?
"Do not be unfair" is pretty vague. Do not lie and do not steal, those are easy recognize and not do. What is fair and unfair is subject to debate, well so are perhaps all precepts but I would say unfairness even more so. 

Who says its unfair to sack an employee? The entire system is unfair if it forces a company to sack anybody. The problem isn't with the individual, not in the scenarios you mentioned anyway. Does an economic system accumulate good and bad karma? They're not sentient so they can't follow precepts. 

Just because a home owner feels awful doesn't mean its unfair. Don't get into the game if you don't want to play, meaning don't make loans if you might not be able to pay them. 

I don't know what Buddhism has to say, but escaping the hassle of financial injustice does seem to be one of the perks of becoming a monk. Maybe the Buddha felt great leaving royal life behind and not having to concern himself with taxes, but this is just speculation.