It can't be a number. These types will just raise prices so $25 is the new $15. Instead the gap needs to be a percentage including bonuses, stocks, health insurance coverage, ...and any other form of compensation. This would mean even business owners or s corp splitters, loan takers against investments, business worth, etc are all taxed fairly and evenly. It would also mean they can't artificial lower their income for tax reasons or for keeping bottom wages low. Additionally cost of living should be factored in such that the median or average value of goods is evaluated by a non biased third party that changes the undisclosed goods for calculating the CoL just so corporations cannot game this.