In most cases, if you withdraw funds from your 401(k) plan before you are 59 1/2, you must pay the 10 percent additional tax on early distributions from qualified retirement plans on any amounts that are not rolled into an IRA. However, there are some exceptions listed in Publication 560, Retirement Plans for Small Business, and Publication 575, Pension and Annuity Income.

References:

• Publication 575, Pension and Annuity Income
• Publication 560, Retirement Plans for Small Business
• Tax Topic 558, Tax on Early Distributions From Retirement Plans
• Tax Topic 412, Lump-Sum Distributions

Source: www.irs.gov