My employer didnt tax bonuses & now ADP is all over me saying we have to do a "gross up". Ive always seen bonuses put in as gross in box 14 on a W2. Cant we just do that?

My employer decided last minute to hand out Christmas bonuses last week.

Each employee received a check for the gross amount, say $200.00...

Now ADP is all over me as if we were trying to escape taxes somehow. I've always used box 14 "other" on a W2 for things like bonuses when I ran payroll in-house. 

Cant we just do it that way?

Or are we forced to do a "gross up" now and make the company pay all the taxes (you can kiss bonuses goodbye if that's the case)