MEMORANDUM **

William and Diane Bonkavich appeal pro se the Tax Court’s decision, following a bench trial, in favor of the Commissioner in their action contesting tax deficiencies for the years 1988 through 1997. We have jurisdiction pursuant to 26 U.S.C. § 7482. We review de novo a Tax Court’s conclusions of law. See Boyd Gaming Corp. v. Comm’r, 177 F.3d 1096, 1098 (9th Cir. 1999). We affirm.

The Tax Court properly sustained the deficiency determination based on Forms 4340 for the years in question. See Hughes v. United States, 953 F.2d 531, 535-36 (9th Cir. 1992). Contrary to petitioners’ contention, the IRS officer is not required to provide them with documentary evidence and copies of statutory notices verifying that all procedural steps were *364properly taken. See Hansen v. United States, 1 F.3d 137,138 (9th Cir. 1993) (holding that Form 4340 is probative evidence in and of itself and, shows in the absence of contrary evidence, that notices and assessments were properly made).

The Tax Court properly held that petitioners waived any challenges to the underlying tax liability by failing to adequately contest it in their petition or at trial. See Tax Ct. R. 34(b)(4); Bob Wondries Motors, Inc. v. Comm’r, 268 F.3d 1156,1161 (9th Cir. 2001).

Petitioners’ remaining contentions lack merit.

AFFIRMED.