¹ Another issue briefed on appeal in our Court was whether SAG's motion requested injunctive relief, such that the magistrate judge would have been without authority to enter a binding order. See 28 U.S.C. § 636(b)(1)(A) (district court may not designate a magistrate judge to determine a motion for injunctive relief). It is unnecessary for purposes of this appeal to reach that issue. Although the district court first addressed the issue of the magistrate judge's authority, its order concludes with the alternative holding that "even if the magistrate judge did not have the authority to deny a motion to stay action, the motion was correctly decided . . . ." Moreover, the district court's order dated April 12, 1995 does not deny "reconsideration" of the magistrate judge's ruling; it states that SAG's motion has been reviewed and that the district court determined that it should be denied. This alternative disposition adequately justifies the conclusion that the district court also reviewed the magistrate judge's disposition de novo. As the parties concede, de novo In this case, the plaintiffs - appellees, Pastorini-Bosby Talent, Inc., and other actors’ agents’ firms, sought to prevent the Screen Actors Guild, a labor union for members of the acting profession, from arbitrating a complaint before an arbitration tribunal. Pastorini-Bosby Talent, Inc. et al, the actors’ agents, filed this action seeking a declaratory judgment that the union has no right to arbitrate its complaint based on the actors’ agents’ conduct and an order staying the arbitration. The union filed a motion to stay the court proceeding. The plaintiffs, actors’ agents, moved for a preliminary injunction enjoining the arbitration. Both motions were referred to a magistrate who denied the union’s motion to stay the court proceedings and held in abeyance the actors’ agents’ motion for a preliminary injunction pending a report from the parties as to the status of the arbitration. The union moved the district court for consideration de novo of the magistrate’s denial of its motion to stay the court proceedings pursuant to 9 U.S.C. § 3. The district court denied the union’s motion, holding that the magistrate had authority to enter the order denying the union’s motion for a stay and that the magistrate had correctly decided the matter. The union appealed to this court. As this Court recognized in a previous appeal, Smith Barney Shearson, Inc. v. Boone, 47 F.3d 750 (5th Cir.1995) the principles necessary to decide a case such as this were set out by the Supreme Court in a series of cases known as the Steelworkers Trilogy: Steelworkers v. American Mfg. Co., 363 U.S. 564 (1960); Steelworkers v. Warrior & Gulf Navigation Co., 363 U.S. 574 (1960); and Steelworkers v. Enterprise Wheel & Car Corp. 363 U.S. 593 (1960). These precepts have served the labor relations community well, and have led to continued reliance on arbitration, rather than strikes or lockouts, as the preferred method of resolving disputes arising during the term of a collective-bargaining agreement. There is no reason either to question their continuing validity, or to eviscerate their meaning by creating an exception to their general applicability. AT&T Technologies v. Communications Workers, 475 U.S. 643 (1986). The second rule is that the question of arbitrability--whether a collective-bargaining agreement creates a duty for the parties to arbitrate the particular grievance--is undeniably an issue for judicial determination. Unless t he parties clearly and unmistakably provide otherwise, the question of whether the parties agreed to arbitrate is to be decided by the court not the arbitrator. AT&T Technologies, supra at 649. The third principle is that in deciding whether the parties have agreed to submit a particular grievance to arbitration, a court is not to rule on the potential merits of the underlying claims. Whether “arguable” or not, indeed even if it appears to the court to be frivolous, the union’s claim that the employer has violated the collective bargaining agreement is to be decided, not by the court asked to order arbitration, but as the parties have agreed, by the arbitrator. Id. at 649-650. “The courts, therefore, have no business weighing the merits of the grievance, considering whether there is equity in a particular claim, or determining whether there is particular language in the written instrument which will support the claim. The agreement is to submit all grievances to arbitration, not merely those which the court will deem meritorious.” American Mfg. Co., 363 U.S. at 568 (footnote omitted); AT&T Technologies, supra at 650. Finally, when the contract contains an arbitration clause, there is a presumption of arbitrability in the sense that “[a]n order to arbitrate the particular grievance should not be denied unless it may be said with positive assurance that the arbitration clause is not susceptible of an interpretation that covers the asserted dispute. Doubts should be resolved in favor of coverage.” Warrior & Gulf, 363 U.S. at 582-583. Such a presumption is particularly applicable where the clause is as broad as the This presumption of arbitrability for labor disputes recognizes the greater institutional competence of arbitrators in interpreting collective bargaining agreements, “furthers the national labor policy of peaceful resolution of labor disputes and thus best accords with the parties’ presumed objectives in pursuing collective bargaining.” Schneider Moving & Storage Co. v. Robbins, 466 U.S. 364 (1984), AT&T Technologies, supra at 650. With these principles in mind, it is evident that the district court erred in not ordering the parties to arbitrate the union’s claim that the actors’ agents’ firms have violated the contract by breaching their fiduciary duties of loyalty to their union member clients by treating them disparately from their non-union clients. Specifically, the union alleged in its arbitration complaint that each of the actors’ agents’ firms “charge non-member performers more than the 10% fee which is the maximum they may charge [union] members, receive fees from employers for the same placement and require such non-[union]member performers to pay for other services as a condition of finding them employment”; that each actors’ agent firm has “acknowledged that it was treating member and non- member clients disparately and reiterated its intent to refuse to eliminate such disparate treatment and honor the Regulations”; that “[t]he disparate treatment of member and non-member performers by [the agents’ firms] violates the fiduciary duty an agent owes all clients and which is incorporated in The issues raised by the union’s complaint against the actors’ agents’ firms are clearly within the ambit of the disputes the parties agreed by contract to submit to arbitration. Section IV(H)(6) provides that the agent firm’s relationship to the union actor shall be that of a fiduciary, and except as otherwise expressly provided, t he firm shall have all the obligations of a trustee as set forth in Sections 2228 through 2239 of the Civil Code of California. Section IV(H)(9) provides that the firm shall owe the duty to the union actor to consider only the interests of the actor in any dealings for the actor, and shall never consider or act upon the interests of the agent when such interests are adverse to the interest of the actor. Section IV(A) provides that every agency contract entered into by an agent firm with any member of the union covering representation in theatrical motion pictures, television motion pictures, and television motion picture commercials shall be in the forms attached and marked “Exhibit E, ”“Exhibit G” and “Exhibit I”. Each exhibit provides that: (i) the collective bargaining agreement (Rule 16(g) of the Screen Actors Guild, Inc.) “which contains regulations governing the relations of its members to talent agents is hereby referred to and by this reference hereby incorporated herein and made a part of this contract; (ii) both parties agree to be bound by the Regulations and by all of the modifications made thereto pursuant to the Basic Contract; (iii) any controversy under this contract ... or as to the existence, execution or validity thereof or the right of either party to avoid this or any such contract or alleged contract on any grounds or the construction, performance, nonperformance, operat ion, breach, continuance or termination of this or any such contract shall be submitted to arbitration in accordance with the arbitration provisions in the Consequently, the contract between the parties is susceptible to the interpretation that the agents’ alleged violations of their fiduciary duties owed the union actors and t he agents’ alleged persistent refusal to remove themselves from conflicts between their own financial interests and that of the union actors have created disputes which the parties agreed to submit to arbitration. Furthermore, the several broad arbitration clauses agreed to by the parties create a presumption of arbitrability that has not been rebutted, because there is no forceful evidence of a purpose to exclude these particular claims from arbitration. The fact that the actors’ agents’ firms refused, after the disputes had arisen, to accept an amendment requiring them to abide by the interpretation of the contract upon which the union’s claim is based does not provide any forceful evidence or positive assurance that the contract between the parties does not plausibly call for the submission of such controversies to arbitration. Even if the district court thought the union’s underlying claim was frivolous, it was that court’s clear duty under the Supreme Court decisions to order the matter submitted to arbitration and to refrain from ruling on the potential merits of the claim.