Who drafts the referendum question?

Political Constitution of Guatemala (Constitución Política de la República de Guatemala) (1985 with amendments in 1993)http://www.constitutionnet.org/files/Guatemala%20Constitution.pdf

Article 173.Referendum Procedure.Political decisions of special significance will have to be submitted to the referendum procedure involving all citizens.The referendum will be called by the Supreme Electoral Tribunal on the initiative of thePresident of the Republic or the Congress of the Republic, which will determine precisely the question or questions to be submitted to the citizens.The Constitutional Electoral Law shall regulate what is relative to this institution.