Issues excluded from being the subject of referendums at the national level

Constitution of 1917 (as amended in 2015)

Article 35

[…]

3. The restriction of the human rights considered in this Constitution, the principles of article 40 therein; the electoral matter; State income and expenses; national security and the organization, operation and discipline of the permanent Army, may not be subject to popular consultation; The Supreme Court of Justice of the Nation will resolve, previous to the call by the Congress of the Union, about the constitutionality on the consultation matter;

Article 40
It is in the will of the Mexican people to constitute into a representative, democratic, secular, federal, Republic, made up by free and sovereign States in everything related to its domestic regime, but united in a federation established according to the principles of this fundamental law.

Federal Law on Popular Referendum (March 14, 2014)

Article 5.  The national significance  topics will be object of the popular referendum.

The national significance of the topics proposed for the popular referendum will be qualified by the majority of the legislators present at each Chamber, with the exception of the referendum proposed by citizens, in that case the Supreme Court of the Nation will resolve on that matter.

The result thereof is binding for federal Executive and Legislative powers as well as for the  competent authorities, when the total participation corresponds at least to forty percent of citizens registered on the voters´ registration list.

Article 11.  The following should  not  be  subject  to popular referendum:
I. Restriction of human rights acknowledged be the Constitution;
II. Principles embodied in Article 40 of the Constitution;
III. Electoral matters;
IV. The revenues and expenses of the State;
V. National security, and
VI.  The organization, operation and discipline of the permanent Military Forces.