When your company receives a fine, a closure, a seizure, or any government action that it considers unfair, the first strategic decision is not "whom do I sue," but what type of defect am I going to claim. 

And that is where a distinction arises that completely defines the defense path: is the act illegal or is it unconstitutional? They are not the same, they are not fought before the same courts, they are not argued in the same way, and they do not produce the same effects. Confusing legality with constitutionality —or choosing the wrong path— can cost you the entire case, not because you were not right, but because you presented it through the wrong channel. 

Understanding this difference is the starting point of any serious defense against the State.

What does it mean to challenge a government action on the grounds of illegality?

Challenging an action for illegality means claiming that the authority violated a secondary law, a regulation, or a procedural rule when issuing its ruling. 

The validity of the rule applied is not questioned, but rather the way in which it was applied. The most common defects of legality are:

• Incompetence: the authority that issued the act did not have the legal powers to do so, by reason of matter, grade, or territory.

• Lack of or improper grounds and motivation: the ruling does not correctly cite the applicable legal provisions or does not explain why the conduct fits into them.

• Procedural defects: the authority omitted essential formalities, such as proper notification or the right to a hearing.

• Improper assessment of evidence or facts: the authority incorrectly interpreted the elements of the case.

• Incorrect application of the law: the authority used a rule that did not correspond to the case.

In these cases, the premise is that the law is fine —it is valid— but the authority applied it incorrectly. 

This type of claim is the natural territory of the contentious-administrative lawsuit or nullity trial before the Federal Court of Administrative Justice (TFJA).

What does it mean to challenge an action on the grounds of unconstitutionality?

Challenging an action for unconstitutionality is something different and deeper: it is claimed that the act —or the rule on which it is based— directly violates the Constitution or the human rights recognized in it and in international treaties. 

Here, we do not only discuss whether the authority applied the law correctly, but whether the law itself, or the act in itself, contravenes the supreme status of the law.

Typical constitutionality issues include:

• Violation of fundamental rights such as property, due process, legal certainty, or the freedom to work.

• Application of a rule that contravenes constitutional principles of legality, equity, or proportionality.

• Imposition of an excessive fine, prohibited by Article 22 of the Constitution.

• Violation of guarantees of a prior hearing before executing a sanction.

The natural territory of constitutionality is the amparo lawsuit, which is the mechanism specifically designed to protect individuals from violations of their fundamental rights by the authority.

What are the key differences between legality and constitutionality?

Can both types of defects be claimed at the same time?

Yes, and in fact, it is one of the most important strategic decisions in defending against government actions. 

In many cases, the same act presents both legality defects and constitutionality arguments, and the strategy consists of deciding how and before whom to assert them.

There are two common scenarios:

1. Legality first, then constitutionality: you go to the nullity lawsuit before the TFJA claiming legality defects and, if the resolution is unfavorable, an amparo lawsuit is brought against that judgment, incorporating the constitutionality arguments.

2. Direct amparo against the act: when the act directly violates fundamental rights and there is a possibility of obtaining a suspension, it may be advisable to go directly to indirect amparo.

The choice between one route or another depends on factors such as deadlines, the possibility of suspending the act, the strength of each type of argument, and the need to exhaust prior resources. 

Comparing which is more convenient between the revocation remedy and the contentious lawsuit is part of this strategic decision, which must be made with a comprehensive vision and not in isolation.

Why does choosing the right path determine the outcome of the case?

The distinction between legality and constitutionality is not an academic exercise: it has concrete procedural consequences that can win or lose the case.

Choosing the wrong path can lead to the court dismissing or throwing out the case without analyzing the merits. For example:

• If an amparo lawsuit is filed without spending the ordinary remedies required by law, it may be declared inadmissible due to a lack of finality.

• If constitutionality arguments are raised before the TFJA, which in principle analyzes legality, those arguments may be left unstudied.

• If deadlines for one path are missed by choosing another incorrect one, the act can become final.

Another decisive element is the suspension of the act. Amparo offers the possibility of suspending the effects of the challenged act while the merits are resolved, which can be vital for a company that needs to keep operating. The availability and conditions of that suspension vary depending on the chosen path, and understanding the scope of the declaration of nullity of an administrative act, its effects, and limits helps to anticipate what is actually obtained at the end of each path.

What role does specialized advice play in this decision?

The border between legality and constitutionality is not always obvious. The same defect can be formulated as a legality defect or as a constitutional violation, and how it is framed determines which court it is litigated in and with what probabilities of success. 

Furthermore, following recent reforms to the amparo framework, which tightened admissibility and suspension requirements, technical precision in choosing the path is more important than ever.

Therefore, advice from a lawyer specialized in public law and litigation against authorities from the very beginning is decisive. It is not just about identifying the defect of the act, but about designing the procedural route that maximizes the chances of annulling the act, suspending its effects, and protecting the company's operation. 

A defense that confuses legality with constitutionality, or that chooses the wrong path, can be right on the merits and still lose due to a presentation error.

Legality or constitutionality: the decision that defines the entire defense

Challenging an authority's act does not begin with drafting the lawsuit, but with a strategic question: am I going to claim that the authority applied the law incorrectly, or that the law or the act violates the Constitution? From that answer, everything else flows: the path, the court, the arguments, the deadlines, and the effects of the eventual ruling.

Legality is contested on the field of the nullity lawsuit before the TFJA; constitutionality, on that of the amparo lawsuit before the Federal Judiciary. Both routes can be combined, but they must be planned with precision. 

Choosing well is the difference between a defense that reaches the core of the matter and one that is dismissed due to a procedural defect. In defending against the State, knowing how to distinguish between the illegal and the unconstitutional is not a technical luxury: it is the foundation of any successful strategy.

Frequently Asked Questions

How do I know if my case is one of legality or constitutionality?

The key question is whether the problem lies in how the authority applied the law, or in the law itself, or in the direct violation of a fundamental right. If the authority was incompetent, did not provide legal grounds for its act, or violated procedure, you are facing a legality defect. 

If the act or the rule applied violates constitutional guarantees such as property, due process, or the prohibition of excessive fines, you are facing a constitutionality challenge. Many cases combine both, so a technical analysis is advisable.

Can the TFJA analyze constitutionality arguments?

The Federal Court of Administrative Justice is primarily designed to analyze the legality of administrative acts. Although it can perform treaty-compliance reviews (control de convencionalidad) in certain cases, challenges of unconstitutionality in a strict sense usually correspond to an amparo lawsuit before the Federal Judiciary. 

Therefore, raising purely constitutional arguments before the TFJA can result in them not being studied, and vice versa. The alignment between the argument and the legal path is fundamental.

Should I exhaust the nullity lawsuit before going to amparo?

In many cases yes, due to the principle of finality (definitividad), which requires exhausting ordinary remedies before resorting to amparo. However, there are exceptions, especially when the act directly violates fundamental rights or when the law allows going to amparo immediately. 

Determining whether you must exhaust the nullity lawsuit first or if you can go directly to amparo is a strategic decision that depends on the type of act and the subject matter, and thus requires specialized analysis.

What happens if I choose the wrong path?

The consequences can be severe. The court may dismiss or throw out the case without examining the merits, either due to inadmissibility, lack of finality, or because the arguments do not correspond to the chosen path. 

Additionally, while you are litigating through the incorrect path, the deadlines for the correct path may expire, leaving the act final and unchallengeable. That is why choosing correctly between legality and constitutionality, and among the different paths, is one of the most critical decisions of the defense.

Is the suspension of the act available in both paths?

Suspension is a characteristic mechanism of the amparo lawsuit, where it can freeze the effects of the challenged act while the merits are being resolved. In the contentious-administrative lawsuit, there are also precautionary measures that can suspend the execution of the challenged act, although under their own rules. 

The availability, requirements, and scope of the suspension vary depending on the path, and this is one of the decisive factors when choosing the path of defense, especially for companies that need to keep operating.

Can I claim legality and unconstitutionality in the same document?

It depends on the path. In the amparo lawsuit, both violations of fundamental rights and, in certain cases, related legality issues can be raised. 

In the nullity lawsuit, mainly legality defects are raised. The frequent strategy is to scale: first the nullity lawsuit for legality and, if unfavorable, the amparo incorporating constitutionality. The optimal way to combine both types of arguments depends on the specific case and the designed procedural strategy.

Which path is faster, legality or constitutionality?

There is no single answer, because it depends on the complexity of the case, the court load, and the appeals that are filed. The nullity lawsuit and the amparo have different duration dynamics. 

What is relevant is not so much which is faster in the abstract, but which better protects the company's interests considering the possibility of suspending the act, the strength of the arguments, and the effects of the judgment. Speed is only one of several factors in the strategic decision.