6. Is there a ban on donations from Trade Unions to candidates?

Artículo 15 - "Prohibiciones. Los partidos políticos no podrán
aceptar o recibir, directa o indirectamente: b) contribuciones
o donaciones de entidades centralizadas o descentralizadas,
nacionales, provinciales,interestaduales, binacionales o
multilaterales, municipales o de la Ciudad de Buenos Aires."

Source: Article 15, Law 26.215: Ley de Financiamiento de los Partidos Políticos, 2007; Article 2, Law 23.298: Ley Orgánica de los Partidos Políticos

The ban referres only to prohibitions towards the political party as an entity, not to the individuals as members. Individual candidates are not allowed to participate in elections, only through political parties. In this sense, parties are the only actor allowed to receive funds and report for their expenses.