They're fined indirectly with stock prices already, but man is your idea really bad.
In terms of dollars, I don't think it would take much to make the point. Suppose you set the fine to 0.5% of salary from all employees. Someone in an entry level job earning $40k would only owe $200. But they'd be really flipping mad and might quit over it. That scales up pretty well - a middle-manager at Facebook who makes $600k would owe $3k. Not enough to really affect their life, but enough to make them really pissed off and potentially bail on the company.
In the end, if we as society want corporations to follow the law, we have to start recognizing that corporations are made up of regular humans following incentives, and if the corporate shield means the people who work in the company and carry out its actions feel no personal consequences of illegal actions, then it's not surprising they'll ignore the law.
That’s the thing I think most people don’t understand about large companies. Money is just a number, they’re playing a game with it. If the company pays a huge fine, all those folks are still rich and nothing bad happens to them, they just have a few different numbers on their spreadsheet. That’s why they don’t care. It’s not like a normal person getting fined, who then loses the opportunity to use their money for things that matter to them.
If we want to hold corporations accountable, we have to issue punishments to corporations that actually hurt their leaders.
I do agree there’s an us/them mentality, but that breaks down when people feel like they can air out their grievances against senior management without sinking the company itself.
Alternatively, start issuing fines such that it’s X percent of revenue plus Y percent of salary from all employees. Even a fine of 1% of annual pay would light a big angry fire under most employees, and perhaps incentivize them to stand up to the execs and refuse to follow illegal or unethical decisions.