Internal Revenue Manual 8.22.2.2.12.2 (10-30-2007)
Section 6702 Frivolous Return Penalties and Questionable W-4 Penalties
1. Frivolous Return Penalties and questionable W-4 penalties do not receive a notice that gives the taxpayer an opportunity to go to Appeals. Therefore, issues involving these penalties may be raised in CDP.
2. A taxpayer may challenge the assessment of the [...]

[25] Reductions in excessive assessments, as opposed to assessments which become legally unenforceable in their entirety, are governed by the abatement statute, 26 U.S.C. § 6404(a):

[26] (a) The Secretary is authorized to abate the unpaid portion of the assessment of any tax or any liability in respect thereof, which -

[27] (1) is excessive [...]