they should be forced to pay a fine and they should have to pay back wages to the employees whose wages they coluded to keep low. Then they should start paying thier employees the wages that they deserve. this goes beyond fare market practices, and there should be strong consequences.
Sometimes the best way for a company to learn not to commit the same offenses again is by imparting a stiff fine on them. This is especially true when the companies are as large and rich as these. The employees that fuel these companies need to be represented and protected from unfair treatment and pay.
It is behavior like that that makes unions so important. Employees should know that there won't be a conspiracy against them to make sure they're not paid market wages. They should have to be sure to pay people what the market will sustain. Fining the companies is the only way to make them behave.