Distributions of after-tax amounts (amounts already taxed) will not be taxable when distributed to you.
However, you will be required to report the amount on your tax return as a non-taxable distribution. The plan should send you a Form 1099-R, which is used to report distributions from retirement accounts. The 1099-R should show the amount as non-taxable. Be sure to provide your tax preparer with a copy of the 1099-R, but first make sure it does not reflect the amount as taxable.
For more information, see Instructions For Forms 1099-R And 5498 on the IRS website.
This question was answered by Denise Appleby