Who decides the final ballot text when the initiative is put to a vote?

Federal Law on Popular Referendum (March 14, 2014)

Article 13. The request for popular referendum may be filed before the Chambers of the Congress accordingly, under the terms of this Law, as of September 1st of the second year of Administration of each legislature and until September fifteenth of the year before Election day.

Article 28. The following shall apply when the request is submitted by citizens:

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IV. After the application of the Chairman of the Executive Board of the corresponding Chamber has been received to verify the constitutionality of the request for popular referendum, the Supreme Court shall:

a)  Resolve  on the constitutionality of the matter of the popular referendum and review that the question directly rises from the matter of the referendum; that is not biased or contains value judgments; uses neutral, simple and comprehensible language; and produces a categorical answer in the positive or negative sense.

b)  Make, where necessary, the corresponding changes to the question in order to guarantee it is consistent with the matter of the referendum and complies with the criteria stated in the previous paragraph.

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Article 29. The resolutions by the Supreme Court shall be final and unassailable.

Article 30. The Call of the popular referendum shall include:

I. Applicable legal grounds;

II. Date of the federal electoral day in which the popular referendum will take place;

III. Brief description of the matter on the national significance topic submitted to the referendum;

IV. The question that will be asked, and

V. Place and date of the release of the Call.