I've come upon a similar scenario. I calculated my withholding using a state/federal tax calculator and then the new tax deal went through and although at my base pay I went from 28% to 24% if I hit my bonus this year, I'll go from 24% to 32%. Ten percent federal income tax increase over a potential $20K bonus. I'm considering asking my boss to limit my bonus to $16,5K keep me at the 24% income level.
I know, it's a first world problem but I'm so tired of the federal government taking more and more of my hard earned dollars without providing affordable health care or infrastructure improvements (i.e. mass transit).
EDIT: And no sooner than posting this I realized I didn't take into account my pre-tax 401k deduction which will spare me going over the 32% $157,500 after all but thanks to this post realize I need to re-calculate my withholdings based upon the 24% tax rate.
*sigh of relief*