On form 8959, what if taxpayer pay less medicare tax than it is supposed to pay?

[kwyp]

Form 8959 is additional medicare tax.

Part V withholding reconciliation, which only reconcile the situation if the medicare withholding is more than medicare tax is.  But what if the taxpayer pay less medicare tax than it is supposed to be? 

For example, medicare withholding is 2000, actual medicare tax is 1800, so the diference is additional medicare tax withholding shown on line 24 on form 8959 and  line 25(c) on 1040

But what if it is on the opposite situation? Such as medicare withholding is 2000, but acutal medicare tax is 2200. Where to enter the shortage of 200 on 1040 form? 

[sjrcpa]

All of the additional Medicare tax computed on Form 8959 will get shown in the 1040 as additional tax.

[PhoebeRoberts]

If your issue is that the W-2 is prepared incorrectly (Box 6 is less than 1.45% of Box 5), the IRS will take that up with the employer.