Most of the revenue collected by the IRS doesn't come from payments submitted with tax returns. It comes from amounts withheld from employees' wages (income tax and payroll tax). Since they represent around 70% of the IRS's revenue, unpaid payroll taxes are taken very seriously.

If you have unpaid payroll taxes, you should address them as quickly as possible before the IRS assesses penalties. You should also be aware that the liability for these taxes is different than almost any other tax — the IRS has broad powers to collect some unpaid payroll taxes from multiple people affiliated with a business.

Payroll taxes are a common name that refers to amounts withheld from employees' paychecks to fund Medicare and Social Security. They are also called FICA taxes (FICA stands for the Federal Insurance Contributions Act, the law that created these taxes).