Why foundational tax doctrines are back on the table
Most tax cases do not change the law. They reinforce it. Courts apply familiar doctrines to familiar fact patterns and move on. That stability is not accidental. It reflects a system that values predictability over precision.
Every so often, though, courts are forced to revisit the foundations because administrative practice drifted and taxpayers adapted. When that happens, the dispute is rarely about one transaction. It is about who decides where discretion ends.
The cases likely to matter most in 2026 share that feature. They test who controls thresholds, definitions, and authority when statutes leave space for agencies to fill.
The cases
Economic substance and relevance
In Liberty Global v. United States, the question is not whether the economic substance doctrine applies; instead, it is who decides when it applies.
§7701(o) states that the two-part economic substance test applies to transactions “to which the economic substance doctrine is relevant.” The district court treated that phrase as surplus. It used the objective and subjective tests without asking whether the doctrine should apply at all.
Taxpayers objected. They argued that Congress preserved a threshold relevance inquiry to protect transactions that intentionally deliver tax benefits without economic substance. The case now sits undecided in the Tenth Circuit after oral argument.
The issue gained urgency after the Tax Court’s unanimous opinion in Patel v. Commissioner. There, the Court rejected the district court’s approach and insisted on a separate relevance inquiry. The Court found relevance in broad terms because other courts had applied the doctrine to similar captive insurance arrangements.
That reasoning clarified little. It did not explain whether a prior application is necessary, sufficient, or merely suggestive. It also left taxpayers without a general rule for predicting when the doctrine would apply.
Several pending Tax Court cases appear ready to follow Patel. That increases the chance of another appellate court weighing in. For now, taxpayers face a doctrine with uncertain boundaries and high penalties.
Limited partners and self-employment tax
A second cluster of cases addresses §1402(a)(13), which excludes a limited partner’s distributive share from self-employment tax.
In Denham Capital, Soroban Capital, and Sirius Solutions, partnerships argued that state-law limited liability should control. The Tax Court disagreed. It adopted a functional analysis that focuses on whether the partner materially participates in the business.
This approach extends self-employment tax beyond what many taxpayers expected. It reaches active partners who enjoy limited liability, regardless of the legal form Congress referenced in the statute.
The implications extend well beyond investment funds. Professional services firms, real estate ventures, and family partnerships all rely on limited liability structures with active owners.
Only Sirius Solutions has been fully briefed and argued on appeal. During the argument, the Fifth Circuit expressed concern about the absence of regulations or clear standards. Treasury once listed guidance under this provision as a priority. It has since gone silent.
If the appellate courts affirm the Tax Court’s approach, taxpayers will operate in a gray zone shaped by litigation rather than guidance. If the courts reject it, they will likely do so because predictability matters more than theoretical purity.
Delegation and deference
The most abstract dispute may prove the most consequential.
Learning Resources v. Trump asks whether Congress delegated too much authority under the International Emergency Economic Powers Act. On its surface, the case concerns tariffs. Beneath that, it concerns limits on delegation.
That question now matters in tax. The Supreme Court’s decision in FCC v. Consumers’ Research signaled renewed attention to the nondelegation doctrine. The Court upheld the delegation there, but it made clear the doctrine still applies. Several justices signaled discomfort with the existing standard.
Tax law relies heavily on broad delegations. §7805 authorizes the Treasury to issue “all needful rules” for enforcing the Code. Treasury often relies on that authority where no specific regulatory grant exists.
After Loper Bright v. Raimondo, the IRS has leaned on §7805 even more aggressively. Without automatic deference to ambiguous statutes, agencies must show that Congress intended to delegate discretion. Section 7805 has become the fallback.
That strategy creates tension. The broader the delegation, the harder it becomes to defend under nondelegation principles.
Foothill Packing v. Commissioner sits at that intersection. The IRS initially defended the regulation at issue solely under §7805. In a supplemental brief, it added a nondelegation defense. The shift suggests institutional awareness that the ground is moving.
The pattern beneath the cases
These disputes share a common feature. They arise when agencies convert flexible standards into default rules.
Economic substance becomes universal rather than contextual. Limited partner exclusions become functional rather than formal. General rulemaking authority becomes a substitute for specific delegation.
Each move increases enforcement power. Each move reduces predictability. Over time, the system drifts from rules that allocate risk to standards that shift it back to taxpayers.
Courts now face pressure to reassert boundaries. Not because agencies acted irrationally, but because incentives pushed them there.
Lessons for practitioners
Threshold questions matter more than substantive tests.
Ambiguity invites administrative expansion before judicial correction.
Bright lines persist because compliance systems depend on them.
Broad delegations work best when courts police their outer edges.
Silence in guidance often signals unresolved institutional conflict.
The human element
Taxpayers plan around text and form. Agencies administer through patterns and experience. Courts arbitrate after the fact. Friction arises when each actor assumes the others see the same incentives. They rarely do.
Forward view
These cases signal a cycle, not a revolution. Courts are reexamining doctrines that grew quietly through practice rather than legislation.
Similar disputes will follow as agencies adapt to reduced deference and courts revisit old assumptions. The system will not snap back. It will recalibrate unevenly, case by case.
Closing thought
When authority stretches without clear limits, courts eventually step in to redraw them.