Short answer. Both. The Labor Code protects an employee who has filed any complaint or instituted any proceeding under the relevant Title, and it separately protects someone who has testified or is about to testify. The protection is not limited to complaints alone — proceedings and testimony are covered as well.
What the law says
It shall be unlawful for an employer to refuse to pay or reduce the wages and benefits, discharge or in any manner discriminate against any employee who has filed any complaint or instituted any proceeding under this Title or has testified or is about to testify in such proceedings.
Labor Code, Article 118 — Retaliation Prohibited. Read the full provision →
Four categories, not one
Article 118 protects an employee who has filed any complaint or instituted any proceeding under this Title or has testified or is about to testify in such proceedings. Read that list carefully: filing a complaint is only the first of four situations named. Instituting a proceeding, having testified, and being about to testify are each listed as their own separate trigger for the article's protection, alongside the complaint itself.
"Instituted any proceeding" is broader than "filed a complaint"
The phrase instituted any proceeding under this Title covers more ground than the word "complaint" alone might suggest to a reader focused only on formal grievances. A proceeding is the broader category, and the article places it on equal footing with filing a complaint. So an employee who initiated some other kind of proceeding under the Title, not framed specifically as a "complaint," is still within what this article protects.
Testimony is protected independently
The article's protection for someone who has testified or is about to testify in such proceedings stands on its own, separate from whether that person filed the complaint or instituted the proceeding themselves. A witness who testifies in someone else's case is covered by this article just as much as the person who brought the complaint or proceeding in the first place.
What this means for you
If your involvement in a workplace matter took the form of a proceeding rather than a formal complaint, or if you testified in a proceeding someone else brought, Article 118's retaliation protection is written to reach you as well. The article does not confine its protection to the single act of filing a complaint, and an employer cannot treat the other three categories as unprotected simply because they are not labeled a complaint.
The Title requirement applies across all four categories
Whether you filed a complaint, instituted a proceeding, testified, or are about to testify, the protection is tied to a complaint, proceeding, or testimony under this Title — the specific portion of the Labor Code Article 118 belongs to. A proceeding or testimony connected to a completely different subject matter is not automatically brought within this article just because it happened at work; the protection's reach is fixed by what the underlying matter concerns, not by which of the four listed categories describes your role in it.