Business can do whatever it wants to do, if it’s a bad idea it won’t survive. It’s a very real and tangible way to demonstrate pay inequality. If you get paid 18% less then everything is (in relative terms) 18% more expensive, in theory, this closes the pay gap.
The problem is a lot of pay inequality is found higher up the chain and this applies the theory to everyone, even low rung employees who are in roles which has pay band based wages. Which creates inequality and resentment.
Either way it’s a very good way of demonstrating pay inequality even if it isn’t done in the most tactful way. The men that are angry about this should reverse the principle and realize this is a thing that exists and how much of an outrage pay inequality is.