Public discussion of the 2027 tax reform is often framed as a conversation about rates. For companies, however, the most consequential issue is not the rate itself but the architecture that determines what may be subtracted from income to arrive at the taxable base. That is where the most relevant debates are taking place, and where early corporate decisions can make a meaningful difference.
For boards and tax teams, the useful exercise is not to wait for the final text. It is to identify which assumptions in their current structures would be exposed if the proposals with the broadest consensus are enacted.
From deduction to traceability
The regulatory trend in Mexico and across the region is not limited to capping specific items. It requires every item to have a verifiable chain of evidence: contract, transaction, payment, accounting record, and economic effect. The question is no longer whether an expense is “necessary” in the abstract, but whether the company can demonstrate why it was necessary, who approved it, and what consideration it received.
That shift has practical consequences:
- Deduction policies must align with operational reality, not only with accounting treatment.
- Supporting documentation must exist at the time of the transaction, not be reconstructed during an audit.
- Internal controls must identify deviations before they become contingencies.
Proposals aimed at limiting certain concepts — payments to related parties, intragroup services, or expenses with diffuse benefits — should not be read in isolation. Their combined effect can materially alter the tax base even if each measure appears limited on its own.
Materiality and economic substance
Materiality has moved from a doctrinal debate to an operational standard. Tax authorities are not only reviewing the formal existence of an entity or contract; they are reviewing whether the structure has substance, whether decisions are actually made where they are said to be made, and whether the people involved have the real capacity to execute them.
In intragroup structures, this requires reviewing:
- Functions and risks. Is the entity receiving the income the one actually performing the functions and assuming the risks?
- Assets and people. Are there sufficient human and material resources to carry out the activity?
- Decisions. Do corporate bodies document relevant decisions and their rationale?
- Remuneration. Does the compensation reflect a market rationale and is it supported by an updated transfer pricing analysis?
The 2027 discussion will likely reinforce the burden of demonstrating these elements. Companies with structures inherited from prior years should review whether operational reality still matches the contractual narrative.
Intragroup transactions: the most sensitive area
Related-party transactions concentrate much of the debate. Not only because of transfer pricing, but because of how services, financing, and the use of intangibles are documented. A signed contract does not replace economic analysis, and a transfer pricing study does not replace evidence that the service was actually provided.
The proposals most likely to remain in the final discussion tend to require:
- Identification of the effective benefit to the recipient entity.
- Evidence of the service and its arm’s-length value.
- Consistency between tax documentation and financial accounting.
- Periodic review of the assumptions used in the analysis.
In practice, many contingencies do not arise from a poorly designed transaction, but from documentation that did not evolve at the same pace as the business.
A review calendar for 2026
The reform will be debated in 2027, but its effects may reach transactions entered into earlier. Preparation should therefore begin now:
- Tax base diagnostic. Identify the most significant items and the quality of their supporting documentation.
- Intragroup structure review. Compare contracts, functions, risks, and operational reality.
- Transfer pricing updates. Confirm that assumptions remain valid.
- Control enhancement. Document approvals, payments, and deliverables.
- Scenario modeling. Assess the impact on cash flow, profits, and compliance under different possible texts.
Conclusion
The 2027 tax reform should be read as a discussion about evidence, not only rates. Companies that anticipate the review of their tax base, materiality, and intragroup documentation will be better positioned to adapt without surprises. Defensible tax planning is not about finding the statutory gap; it is about building a position that can be explained through consistent facts, contracts, and numbers.
The best tax defense is an operation that can be described without contradictions: what was said, what was documented, and what actually happened.