Defacto it pretty much is a maximum wage law as no company is going to pay employees over the "cap" only to be slammed with an obviously punitive tax (on top of existing payroll, sales, and corporate income tax).  Companies will cut salaries (or offer alternative compensation) to avoid the tax and the "tax" will produce no significant revenue but the government will have to already know that will be the outcome and thus the "tax" isn't intended as a tax at all but a method of control.