I am not a lawyer so feel free to tell me if and why this wouldn't work but…
What if a law was passed that, say, 20% of the end of year profits of every company have to be split equally and then added to the pay of every single employee in the company for the next year.
The employees wouldn't own that part of the company so would have no say at board meetings but it would give a concrete reason for them to care for the profitability and expansion which seems like a win win. Happy employees make for a more profitable business.
Better yet, have the union own that 20% even though they wouldn't be getting the dividends (not sure if I used that word correctly but you probably get my drift). They could be the ones to have a say in the board meetings.
[Edit : spelling]