In this context, "Demanda colectiva y acción de clase" is translated as "Acción de clase" because it refers specifically to a class action lawsuit.

Example sentences:
1. Presentaron una acción de clase contra la empresa por prácticas laborales injustas.
(They filed a class action lawsuit against the company for unfair labor practices.)
2. La corte dictaminó a favor de los demandantes en la acción de clase.
(The court ruled in favor of the plaintiffs in the class action.)

representative action : one party, including a body or organis/zation, brings a claim on behalf of a group who can then join in: an opt-in scene in the UK

demanda colectiva : class action, Alcaraz & Hughes + 'synonym: acción de grupo, Col.. ' West -> acción de clase, no entry in either.

BUT class action : a number of plaintiffs or complainants bring and join in the suit, on an express opt-in in the UK vs. *automatic opt-in*, so express opt-out needed in the USA for known 'victims' : source > per Pamela B.,a or the top Washington DC civil litigator at a recent law conference in Madrid.

The difference in English law used to be well explained in the erstwhile HLT / Holborn Law Tutors College Civil Procedure / Litigiation Manuals.

I hope this is helpful:
Collective Action Different from Class Action
Collective actions share some characteristics with class actions, but are not the same. In FLSA cases, an employee must opt in, meaning that they must affirmatively sign a document stating that they wish to be a part of the lawsuit. In class actions, under Rule 23(b) of the Federal Rules of Civil Procedure, employees are presumed to be a part of the class and any employee who doesn't want to participate in the lawsuit must opt out. Class actions cannot be used to assert wage and hour claims brought under the FLSA but employees may bring an "opt in" or "collective action" under FLSA Section 216(b). One or more employees may maintain an action, on behalf of themselves and other employees who are similarly situated, to recover damages on any of the grounds available for individual FLSA relief. Employees who do not file a written consent are not bound by the outcome of the collective action and may file a subsequent private action. The FLSA collective action may be brought in either state or federal court.
Class & Collective Actions
http://www.touhylaw.com/class-and-collective-actions.php
A class action is a lawsuit in which one or a few individuals represent a large group of individuals with similar claims. There are four basic requirements for a class action:
a. Numerosity. The class must be so large that joining all the members in the case would be impracticable (usually this means more than 40).
b. Commonality. The class must have claims that are based on similar facts and legal theories. Usually, these similarities must also predominate over any differences in class members’ claims.
c. Typicality. The representative plaintiff or plaintiffs’ claims must be typical of the other class members’ claims.
d. Adequacy. The representative plaintiff or plaintiffs’ interests must be aligned with the other class members’ interests and must be represented by attorneys who are capable of managing a class action.
A collective action is similar to class action but is used in specific kinds of employment disputes and has several significant differences. The most important difference is that members must join or “opt-in” to a collective action by filing a written consent form in the court in which the action is pending. Because members must take affirmative action to join a collective action, the statute of limitations runs on each member’s claims until the written consent form is filed.

Class and collective actions spread the cost of litigation among many people and conserve judicial resources by allowing many claims to be adjudicated in a single proceeding. Class and collective actions also provide a remedy when many people have small claims that would otherwise be too expensive to litigate.