The Fayette County Board of Commissioners (Commissioners) appeals from an order of the Court of Common Pleas of Fayette County (trial court) that confirmed the award of an arbitrator determining that the discharge of a county corrections officer by the Fayette County Prison Board (Prison Board) was a matter subject to arbitration and that, although Fayette County (County) had just cause to discipline the officer, the penalty of discharge was excessive. The sole question presented is whether the grievance arbitration award must be vacated for lack of jurisdiction and/or arbitrability because the underlying discharge was an exercise of the Prison Board’s inalienable statutory powers.
I
The Prison Board is made up of all three County Commissioners, a judge of the trial court, the Sheriff, the District Attorney and the County Controller, pursuant to Section 1 of the Act of May 16, 1921, P.L. 579, as amended, 61 P.S. § 408. The American Federation of State, County and Municipal Employees, Council 84 (AFSCME), is the certified collective bargaining representative for County corrections officers. The Commissioners are the exclusive representative for negotiating collective bargaining agreements and processing grievances for the Prison Board, as well as for judges and all other elected or appointed county officers having employment powers, pursuant to Section 1620 of The County Code, Act of August 9, 1955, P.L. 323, as amended, 16 P.S. § 1620. The Board of Commissioners and AFSCME entered into a collective bargaining agreement effective January 1,1994.
The Prison Board voted to terminate Corrections Officer William Prinkey; AFSCME filed a grievance asserting a lack of just cause. Before the arbitrator, the County litigated the merits of the just cause issue and also challenged the arbitrability of the *275termination, arguing that authority over discharges was reserved exclusively to the Prison Board under Section 4 of the Act of May 16, 1921, 61 P.S. § 411. Section 4 provides in part that “[a]ll deputies, assistants, or keepers ... may at any time be suspended by the warden or removed by the said board.” The County further argued Prison Board exclusivity under Section 1620 of The County Code, which provides that the exercise of the commissioners’ function as exclusive representative for other county officers “shall in no way affect the hiring, discharging and supervising rights and obligations with respect to such employes as may be vested in the judges or other county officers.”
The arbitrator noted that the collective bargaining agreement expressly provides in Article XIV, Section I, that “[t]he County shall not discharge nor suspend any employee without just cause,” and provides in Article XIV, Section 2, that “[a]n employee may grieve a discharge beginning with Step 3 of the grievance procedure.” Arbitrator’s Opinion and Award, p. 16. Article XXIV provides for arbitration as the fourth step of the grievance procedure. The arbitrator concluded that the parties intended to negotiate a just cause provision for discipline of employees and that they agreed to dispute resolution procedures including arbitration of discharges. He concluded further that such an agreement was consistent with statutory law and court precedent.
The Commissioners appealed, challenging only the determination as to arbitrability. The trial court, citing Community College of Beaver County v. Community College of Beaver County, Soc’y of the Faculty (PSEA/NEA), 473 Pa. 576, 375 A.2d 1267 (1977), stated that judicial review of a public sector labor arbitration award is limited. The award must be confirmed by a reviewing court so long as the arbitrator’s decision can in any rational way be derived from the collective bargaining agreement, viewed in light of the language, context and any other indicia of the parties’ intention. The trial court cited Leechburg Area School Dist. v. Dale, 492 Pa. 515, 424 A.2d 1309 (1981), and Scranton Fed’n of Teachers, Local 1147, AFT v. Scranton School Dist., 498 Pa. 58, 444 A.2d 1144 (1982), for the proposition that the review described in Community College of Beaver County, known as the “essence test,” extends to an arbitrator’s decision regarding arbitrability. Applying that test, the trial court concluded that the terms of the agreement encompassed the subject matter of the dispute and that the award arose from the essence of the agreement.1
II
The threshold question is the nature of this Court’s review, a point on which the parties differ sharply. The Commissioners quote from Section 7302 of the Uniform Arbitration Act, 42 Pa.C.S. § 7302:
(d) Special application.—
(1) Paragraph (2) shall be applicable where:
(ii) A political subdivision submits a controversy with an employee or a representative of employees to arbitration.
(2) Where this paragraph is applicable a court in reviewing an arbitration award pursuant to this subehapter shall, notwithstanding any other provision of this sub-chapter, modify or correct the award where the award is contrary to law and is such that had it been a verdict of a jury the court would have entered a different judgment or a judgment notwithstanding the verdict.
They refer also to Section 7314(a)(1), 42 Pa. C.S. § 7314(a)(1), which provides that a court shall vacate an award where “(iii) the arbitrators exceeded their powers_”
The Commissioners argue that the question of the arbitrability of the grievance dispute is not derived from the collective bargaining agreement but rather is derived from statutory and constitutional law. They contend that the review of issues of law, jurisdiction and arbitrability is the same as review of *276a verdict non obstante veredicto, citing County of Centre v. Musser, 519 Pa. 380, 548 A.2d 1194 (1988). Without citation, the Commissioners assert that the “essence test” cannot apply to the threshold question of the legal enforceability of the collective bargaining agreement or the jurisdiction of the arbitrator.
The Commissioners note that Article XXV of the collective bargaining agreement states that the parties’ intent is that the agreement comply with all statutes, regulations and judicial decisions and that, if it or any portion of it is determined by proper authority to be in conflict with them, the agreement shall automatically be adjusted to comply. Article XXVI states that if any terms are found invalid or declared unenforceable by federal or state statute or regulation or by a decision of a court, such determination shall not affect any other terms. The Commissioners contend that these provisions show that the parties contemplated that terms of the collective bargaining agreement could be superseded by legislative or judicial actions. They aver that where statutes governing removal of employees exist, the courts have not hesitated to hold that grievance arbitration awards are invalid and unenforceable, without regard to the collective bargaining agreement provisions or the facts of a particular case.2
The Commissioners acknowledge that the question of the arbitrability of a matter in dispute must first be tested by grievance arbitration, citing Section 903 of the Pennsylvania Employe Relations Act (PERA), Act of July 23, 1970, P.L. 563, as amended, 43 P.S. § 1101.903, and Pennsylvania Labor Relations Board v. Greater Johnstown Area Vocational-Technical School, 48 Pa.Cmwlth. 604, 410 A.2d 1290 (1980). Because that procedure has been followed in this case, the Commissioners assert, again without citation, that this Court should now review the merits of their challenge, which relate to various constitutional and statutory provisions.
The Court concludes that the Commissioners’ attempt to alter the settled law in regard to review of public sector grievance arbitration awards must fail. In Scranton Fed’n of Teachers, 498 Pa. at 65, 444 A.2d at 1147, the court held: “It is clear that the broad judicial deference given arbitrators’ decisions applies with equal force to determinations regarding the arbitrability of the subject matter of a grievance.” In County of Centre v. Musser the Supreme Court held that this Court correctly concluded that “essence test” review as set forth in Community College of Beaver County applied to judicial review of an arbitration award relating to the dismissal of prison guards. The Court expressly noted that, although Community College of Beaver County interpreted and applied a provision of a superseded statute relating to arbitration, Section 7302(d)(2) of the Uniform Arbitration Act was substantially a reenactment of the earlier provision. Therefore “essence test” review remained applicable under Section 7302(d)(2).
In the present ease, there can be no dispute that the arbitrator’s conclusions concerning the arbitrability of a grievance over discharge of a corrections officer is rationally derived from the terms of the agreement and draws its essence from that agreement. Indeed, the Commissioners do not contend otherwise. In view of the exceedingly clear language of Article XIV, providing that an employee may grieve a discharge, and Article XXIV, providing for arbitration as the fourth step of the grievance procedure, a conclusion to the contrary would be suspect under essence test review. Accordingly, this Court must affirm the trial court’s order confirming the arbitrator’s award.
Ill
The Court observes that an alternative basis exists on the face of this record for affirming the trial court’s order. AFSCME raised before the arbitrator, the trial court and this Court the question of *277whether the Commissioners should be es-topped from advancing a claim that a provision of the collective bargaining agreement to which they voluntarily agreed should not be enforced because it is illegal. Neither the arbitrator nor the trial court addressed this issue, but AFSCME has preserved it for review.
In Pittsburgh Joint Collective Bargaining Comm. v. City of Pittsburgh, 481 Pa. 66, 391 A.2d 1318 (1978), the city refused to proceed to binding arbitration in a grievance over a discharge. The union filed a complaint in equity seeking to compel the city to submit to arbitration. The chancellor sustained the city’s preliminary objections based upon an assertion that such arbitration was in conflict with provisions of the Civil Service Act, Act of August 5, 1941, P.L. 752, as amended, 71 P.S. §§ 741.1 — 741.1005, and that proceeding to arbitration was therefore prohibited by Section 703 of PERA, 43 P.S. § 1101.703. The Supreme Court held that the city could not assert that defense in that context to avoid compliance with the agreed upon arbitration procedure, and it expressly declined to address the question of whether the agreement was in conflict with the Civil Service Act. The Court stated:
To permit an employer to enter into agreements and include terms such as grievance arbitration which raise the expectations of those concerned, and then to subsequently refuse to abide by those provisions on the basis of its lack of capacity would invite discord and distrust and create an atmosphere wherein a harmonious relationship would virtually be impossible to maintain.
Pittsburgh Joint Collective Bargaining Comm., 481 Pa. at 74, 391 A.2d at 1322. See also Grottenthaler v. Pennsylvania State Police, 488 Pa. 19, 410 A.2d 806 (1980) (inclusion of retirement benefits in two collective bargaining agreements after the effective date of the state retirement statute constituted waiver of any bar to collection of such benefits under the exclusivity provision of the statute during the terms of those agreements).
In City of Scranton v. Local Union No. 669 of the Int’l Ass’n of Fire Fighters, AFL-CIO, 122 Pa.Cmwlth. 140, 551 A.2d 643 (1988), the city petitioned to set aside an award of arbitrators on the grounds of illegality of various provisions. Acknowledging that arbitrators may not mandate that a public employer perform an illegal act, this Court differentiated between new provisions of the award and those that were simply carried over from previous agreements into which the city had entered voluntarily. “The arbitrators’ mandate, however, must be distinguished from a situation where an employer voluntarily agrees to perform an act. Where it does so it cannot later contend that the act is illegal and refuse to perform it; indeed, it will be estopped from doing so.” City of Scranton, 551 A.2d at 646 (citing Grottenthaler, Fraternal Order of Police, E.B. Jermyn Lodge # 2, by Tolan v. Hickey, 499 Pa. 194, 452 A.2d 1005 (1982) (plurality opinion)). The Court noted that a public employer who came to believe that a term of its collective bargaining agreement was illegal could not raise illegality as a defense to an award or to the existing agreement but could bargain to have that provision removed from future agreements.
In the present case the Commissioners’ sole claim before the trial court and this Court was and is that provisions of the collective bargaining agreement to which they voluntarily agreed are illegal. Under the authorities noted above, the Commissioners are estopped from advancing such a claim. Therefore, the order of the trial court confirming the arbitrator’s award must be affirmed on this basis as well.3
ORDER
AND NOW, this 2nd day of April, 1997, the order of the Court of Common Pleas of Fayette County is affirmed.
. Following an initial opinion issued by a panel of this Court on July 19, 1996, reversing the order of the trial court, AFSCME applied for and was granted reargument before the Court en banc.
. Of the several cases referenced by the Commissioners in support of this assertion, only one, Neshaminy Fed’n of Teachers v. Neshaminy School Dist., 501 Pa. 534, 462 A.2d 629 (1983), involved review of an arbitrator’s award following the grievance of a removal. The Supreme Court applied "essence test” review and closely examined the terms of the collective bargaining agreement to conclude that the arbitator’s award reinstating the teacher did not draw its essence from the terms of the agreement and should be set aside.
. In view of the reasons stated for the disposition, the Court may not and does not express an opinion on the question of whether the just cause and arbitration provisions of the collective bargaining agreement conflict with statutes relating to counties and penal institutions, although this issue was argued by several amici curiae as well as by the parties.