Hello and thank you for using Just Answer,Income tax is withheld from the pay of most employees. Your pay includes your regular pay, bonuses, commissions, and vacation allowances. It also includes reimbursements and other expense allowances paid under a non-accountable plan.
When you start a new job, you must fill out IRS Form W-4 and give it to your employer. Your employer should have blank copies of the form. If you need to change the information later, you must fill out a new form. You also would have withholding on any Flexible spending accounts and loans made from your 401K or retirement.
Some companies also offer to withhold for charitable contributions.
If you know your employer has withheld an amount and you do not know what it was for then you should ask them about the withholding.
Any withholding should have been authorized and understood by the employee.