This disparity just gets bigger all of the time. 18% will have to suffice for our purposes.
Can you imagine the effect if everyone was getting paid equitably and equally? Then imagine someone suggesting that we impose a unilateral 18% tax on women. Someone would run to get the tar and feathers!
There is no reason what-so-ever that congress can't solve this immediately. The reason we know about the disparity is because we know who is getting paid and how much they are paid. That means we know who needs to get with the program. FIX IT NOW!