How does the HR system ADP define the % federal tax to be withheld? In case the salary increases, is it possible that the taxes are not withheld properly?

[MaryK4]

The payroll deductions are calculated using the IRS tables and any additional withholdings as indicated on the W4.  If your salary increases, the tax withholding is adjusted in their system based on what the projected year end amount would be.  It may be possible that withholding is incorrect, this most likely would occur if there was an entry error.  

[lericardo]

It seems that the system is withholding much less federal taxes than expected, and now I will need to pay at once during the taxes filing process. I guess that something might be wrong in ADP, and I don't know what.