What should I do if my employer did not withhold the right amount of tax?

If your employer didn’t withhold the correct amount of taxes from your wages and they remain unpaid, it could affect the amount of Social Security, Medicare, or unemployment benefits you receive in the future.

It’s recommended that you discuss the error with your employer and work out an agreement as soon as possible. The employer should withhold the correct amount of taxes from your wages, but until the IRS receives the additional tax that needs to be paid, you may be required to pay the difference.

You can use the withholding calculator offered by the IRS to see if your withholdings are correct for your paycheck. You can also contact your local Social Security Administration to update your withholdings.
Source: irs.gov