Jay and Elizabeth Karpa appeal from the Tax Court’s decision upholding the Commissioner’s proposed imposition of a tax penalty under former I.R.C. § 6661(a). The Karpas argued that the § 6661(a) tax penalty for substantial understatement of tax liability, as applied retroactively to their 1984 return, was unconstitutional as violative of the ex post facto clause. Both parties moved for judgment on the pleadings, and the Tax Court granted the Commissioner’s motion. We agree that former § 6661(a) does not violate the ex post facto clause and therefore affirm.
I
The Commissioner audited the Karpas’ 1984 joint tax return and determined a deficiency of $10,933.07, an understatement of their tax liability of approximately 18%. 1 The Karpas paid this amount, plus applicable interest, in July 1986. The Commissioner issued the Karpas a statutory notice of deficiency and proposed a 25% penalty, pursuant to I.R.C. § 6661, for substantial understatement of tax liability for the year 1984. Recent amendments to the Internal Revenue Code (Code) had increased the penalty for substantial understatement of tax liability from 10% of the underpayment to 25% of the underpayment, to be applied to penalties assessed after the effective date of the amendments, October 21, 1986. The Commissioner therefore sought to assess a $2,733.27 penalty under § 6661(a), 25% of the $10,933.07 understatement. The Commissioner also asserted that the Karpas were liable for additions to tax pursuant to former I.R.C. § 6653(a)(1), (2) 2 for negligence.
The Karpas petitioned the Tax Court for redetermination of the deficiency. They challenged only the imposition of the 25% penalty under § 6661(a), arguing that retroactive application of the increase to their 1984 tax return violated the ex post facto clause. The Commissioner moved for judgment on the pleadings, and the Karpas filed a cross-motion for judgment on the pleadings.
3
The Tax Court followed the established rule that the ex post facto clause applies only to criminal statutes and rejected the Karpas’ contention that § 6661 as amended was criminal in nature. Relying on
United States v. Halper,
—U.S.-,
This appeal followed and presents an issue of first impression. The Karpas continue to press their ex post facto argument and, for the first time, raise the contention that retroactive application of the increased penalty under § 6661(a) violates their rights to due process and equal protection of the laws. After reviewing the relevant statutory history of § 6661, we will address the constitutional challenges to the statute.
II
A
Section 6661(a) of the Code, originally passed in 1982 and applicable to tax *786 returns due after December 31, 1982, penalizes the “substantial understatement of income tax.”
If there is a substantial understatement of income tax for any taxable year, there shall be added to the tax an amount equal to 25 percent of the amount of any underpayment attributable to such understatement.
I.R.C. § 6661(a) (repealed 1989). As enacted in 1982, § 6661(a) provided for a 10% addition to tax liability. In 1986, Congress passed § 8002 of the Omnibus Budget Reconciliation Act of 1986 (OBRA 1986), increasing the additional assessment from 10% to 25%. OBRA 1986, Pub.L. 99-509, § 8002(a), 100 Stat. 1874; 1951 (1986). The amendment was to apply to “penalties assessed after the date of the enactment of this Act.” Id. § 8002(b). 4
The legislative history of § 6661 indicates that the principal objective of the section was to deter taxpayers from playing the “audit lottery,” that is, taking undisclosed questionable reporting positions and gambling that they would not be audited. See S.Rep. No. 494 (Vol. 1), 97th Cong., 2d Sess., 272-73 (1982), reprinted in 1982 U.S.Code Cong. & Admin.News 781, 1019-1020. 5 The Senate Report accompanying OBRA 1986 indicates that a primary purpose of the act was to reduce the budget deficit. S.Rep. No. 348, 99th Cong., 2d Sess. 3-4, U.S.Code Cong. & Admin.News 1986, 3607. Section 8002, which amended I.R.C. § 6661(a) to increase the tax penalty for substantial understatement of income tax liability, was passed along with other revenue enhancing measures in title VIII, subtitle A, of OBRA 1986.
B
The Karpas challenge the amendment to § 6661(a) as an unconstitutional ex post facto law. Because the 25% penalty applied to penalties
assessed
after OBRA 1986 was enacted, the increased penalty can apply, as in this case, retroactively to returns due after December 31, 1982, when § 6661 first became effective, but before OBRA 1986 was passed by Congress. This retroactive application of an increase in punishment they claim violates the ex post facto clause.
See Collins v. Youngblood,
—U.S. -, --,
The prohibition against ex post facto laws applies only to penal legislation
*787
that imposes or increases
criminal
punishment for conduct predating its enactment.
See, e.g., Harisiades v. Shaugknessy,
The Court has also warned, however, that the constitutional prohibition against ex post facto legislation may not be avoided by giving civil form to criminal legislation.
See Burgess v. Salmon,
97 U.S. (7 Otto) 381, 384,
In
Helvering v. Mitchell,
The Court’s most recent discussion of the distinction between a civil penalty and criminal punishment is contained in
United States v. Halper,
—U.S.-,
C
We agree with the Tax Court that the increased tax penalty imposed under former § 6661(a), as amended by § 8002 of OBRA 1986, is a civil sanction; the ex post facto prohibition is not implicated. Under
Bankers’ Trust,
The Karpas’ reliance on Burgess v. Salmon is misplaced. The Court there concluded that the ex post facto clause prohibited the government from retroactively increasing the tax that had to be paid to avoid a criminal penalty. Here, no such criminal sanction was implicated. The Kar-pas’ conclusion that characterization of § 6661(a)’s addition to tax as a “penalty” is dispositive and requires reversal of the Tax Court is similarly misplaced. Section 6661(a) imposed a civil sanction, raising no ex post facto concerns.
Ill
For the first time on appeal, the Karpas argue that retroactive application of the increased tax penalty under § 6661(a) violates their rights to due process and equal protection of the law. We decline to consider this belated argument, following our general rule that new theories ordinarily will not be considered for the first time on appeal.
See, e.g., National Wildlife Fed’n v. Hanson,
IV
For the foregoing reasons, the judgment entered by the Tax Court for the Commissioner is affirmed.
AFFIRMED.
Notes
. The Commissioner apparently disallowed substantial deductions taken by the Karpas.
. At the time, I.R.C. § 6653 provided, in relevant part:
(a) Negligence.—
(1) In general. — If any part of any underpayment ... is due to negligence or disregard of rules or regulations, there shall be added to the tax an amount equal to the sum of— (A) 5 percent of the underpayment, and
(B) an amount equal to 50 percent of the interest payable under section 6601 with respect to the portion of such underpayment which is attributable to negligence for the period beginning on the last date prescribed by law for payment of such underpayment. ...
I.R.C. § 6653(a)(1) (1987).
.See Rule 120, Rules of Practice and Procedure of the United States Tax Court, 26 U.S.C. foil. § 7453.
. Congress actually passed two acts in 1986 that would have amended § 6661(a). In addition to § 8002 of OBRA 1986, the Tax Reform Act of 1986 (TRA 1986) would have increased the additional assessment from 10% to 20%, but was to apply only prospectively to returns due after December 31, 1986. TRA 1986, Pub.L. 99-514, § 1504, 100 Stat. 2085, 2743 (1986). OBRA 1986 § 8002(c) “repealed" TRA 1986 § 1504, and the Technical and Miscellaneous Revenue Act of 1988, Pub.L. 100-647, § 1015(c), 102 Stat. 3342, 3569 (1988), made clear that the 25% penalty applied under I.R.C. § 6661(a).
See also Pallot-tini v. Commissioner,
Section 6661 was repealed by the Omnibus Budget Reconciliation Act of 1989 (OBRA 1989). OBRA 1989, Pub.L. No. 101-239, § 7721(c)(2), 103 Stat. 2106, 2399. The "substantial .understatement” penalty was consolidated along with other "accuracy-related penalties" in I.R.C. § 6662. See id. § 7721(a). The new law applies to returns due after December 31, 1989. Id. § 7721(d).
. The Senate Report indicates:
The committee believes that an increasing part of the compliance gap is attributable to the "audit lottery." The audit lottery is played by taxpayers who take questionable (although non-negligent) positions not amounting to fraud or negligence on their returns in the hope that they will not be audited. If a taxpayer is audited and the questionable position is challenged, then he or she pays the additional tax owing plus interest. Importantly, however, táxpayers are not exposed to any downside risk in taking highly questionable positions on their tax returns since even resolution of the issue against the taxpayer will require only payment of the tax that should have been paid in the first instance with interest to reflect the cost of the “borrowing.” ... Thus, in the event that the questionable position is not detected, the taxpayer will have achieved an absolute reduction in tax without cost or risk. The committee believes, therefore, that taxpayers should be subject to a penalty designed to deter the use of undisclosed questionable reporting positions.
S.Rep. No. 494 (Vol. 1), 97th Cong., 2d Sess., 272-73 (1982), reprinted in 1982 U.S.Code Cong. & Admin.News 1019-1020.
. The statute did allow for proportionate reduction in tax liability upon a satisfactory showing that state or local tax had been paid on the property for some portion of the five-year period preceding the decedent’s death.
. The Karpas question how retroactive application of an increased penalty can have a deterrent effect. Though emphasizing the statute’s deterrent effect would seem, under Halper, to be in the Karpas’- interest, we note that taxpayers who have taken questionable reporting positions might be persuaded by the increased sanction to come forward before they are audited. Cf. Treas.Reg. § 1.6661-6(c) (1990) (Commissioner will waive penalty for substantial understatement of income if taxpayer shows additional amount of tax or adequately discloses position in amended return filed before contact initiated).
