How do I create an additional paycheck to correct Union vacation benefit amount which affected the taxes withheld?

I'd be glad to help with your payroll question, LTDB.

You can create an unscheduled payroll to add the remaining amounts of the union vacation benefit. Here's how:

1. Go to the Employees menu and click Pay Employees. 
2. Select Unscheduled Payroll
3. Make sure that the Pay Period Ends date, Check Date, and Bank Account are all correct.
4. Click Open Paycheck Detail to enter the additional union vacation benefit amount. 
5. Select Save & Next to go to the next employee, or select Save & Close to go back to the Enter Payroll Information window.
6. Follow the succeeding steps to create the additional paycheck. 

Here's an article for more details: How Do I Create a Paycheck for an Employee?

I'd also like to share these articles for additional guidance in case you need them in the future: 

• Delete or Void Employee Paychecks
• Reduce Paycheck Wages For an Employee Who has Been Overpaid

Don't hesitate to reply to me or post new questions in the Community if you need more help with QuickBooks. We're always here to provide assistance again.