If you take a withdrawal from a 401k, 10% is automatically withheld for Federal taxes. Normally, there's an additional 10% withheld as a penalty for early redemption (applies if you are under age 59-1/2). That additional 10% penalty is being waived by Congress due to COVID-19.
WARNING: Withdrawal from a 401k becomes TAXABLE INCOME to you. You will owe Federal and State (if applicable) income tax on the 401k proceeds, unless it's from a "Roth 401k", which most of you don't have. The 10% withholding usually IS NOT enough, you may end up in the humiliating and painful position of having to write a check to the IRS for extra taxes due.