Opinion by
Me. Justice Jones,The question in this case is whether the City of Philadelphia, in the trespass action here involved, waived its defense of liability for workmen’s compensation when it did not formally raise the employer-employee relationship between it and the plaintiff’s decedent until the plaintiff issued a mandamus execution to obtain satisfaction from the City of her judgment recovered against the City and the other defendants jointly.
The plaintiff is the widow and personal representative of Stanley A. Socha who died as a result of injuries received in a collision between a sanitation truck of the City, upon which he was riding, and an automobile operated by the original defendant, Ernest Metz. Metz joined Hugh P. Brown, the driver of the City’s truck, and the City of Philadelphia as additional defendants. The original defendant’s complaint against the City of Philadelphia, as additional defendant, alleged that the “collision was directly, proximately and solely due to the carelessness, recklessness and gross negligence of the servant, agent or employee of the addition defendant, City of Philadelphia, in operating its aforementioned motor vehicle” and that by reason thereof the “additional defendant, City of Philadelphia, is either solely liable to plaintiff, . . . jointly and severally liable to them with defendant, or liable to defendant... in whatever amounts defendant . . . may be held liable to plaintiff ... on the causes of action declared by her . . . .”
Trial of the negligence issue and liability therefor was had which resulted in a jury’s verdict for the plaintiff against all defendants jointly in the sum of $40,000. Motions for new trial filed by Metz and the City of Philadelphia were refused and judgment was entered on the verdict. No further motions were made, and no *635appeal was taken by either the defendant or the additional defendant, City of Philadelphia. The plaintiff collected $15,000 from Metz’s insurance carrier on account of her judgment and caused a writ of mandamus execution to issue against the City of Philadelphia for the balance of the judgment. The next day the City petitioned the court to quash the writ of mandamus execution and to have the judgment marked satisfied of record as to it. A rule was entered on the plaintiff to show cause why the prayers of the petition should not be granted, all proceedings against the City on the judgment to stay meanwhile.
Paragraph 2 of the City’s petition to quash the writ, etc., averred “That at the time of the alleged accident, the said Stanley A. Bocha, deceased, was in the employ of the City of Philadelphia as a helper on its said garbage truck, as will more fully appear in the Notes of Testimony filed in this case, which are herein incorporated by reference and made a part hereof.” The notes of the testimony taken at the trial of the trespass action plainly reveal that, at the time the plaintiff’s decedent received his mortal injury as a result of the collision, he was an employee of the City acting in the course of his employment.
For answer to the above-quoted averment of the City’s petition to quash, the plaintiff merely averred argumentatively that “the allegations of paragraph two of the petition are irrelevant and immaterial for reasons hereinafter more fully set forth in this answer to said petition; that this proceeding by way of petition to quash the mandamus execution and to cause judgment against the City of Philadelphia to be marked satisfied is improper and without authority or warrant in law.”
Within some three weeks of the accident, the City forwarded to the attorney for the plaintiff a compensa*636tion agreement to be executed by her and filed with the Pennsylvania Workmen’s Compensation Board which the plaintiff refused to sign. The plaintiff’s answer admitted these facts but endeavored to obviate their effect by pleading her own legal conclusions.
It is the City’s contention that the plaintiff’s decedent and the City were subject to the Workmen’s Compensation Act; that the plaintiff could not maintain a separate action of trespass against the City; that the joinder of the City as an additional defendant was permissible only to the original defendant to protect his right of contribution from the City in the event they were held jointly liable for the accident; and that, in such circumstances, action by the City to have the judgment against it marked satisfied upon payment of its liability for compensation is the appropriate and only available procedure open to the employer City.
On the other hand, the plaintiff contends that the City’s action is a collateral attack on the judgment entered against it and an effort to litigate and raise a defense of “limited liability” which could and should have been raised in the pleadings or at the trial of this matter or by way of a motion for judgment n.o.v. or any other proper proceeding within the term of court. In short, the plaintiff argues that the City waived its defense of liability for workmen’s compensation.
The court made the rule absolute and ordered (1) that the writ of mandamus execution be quashed and (2) that the judgment entered in favor of the plaintiff be satisfied of record as to the City of Philadelphia upon payment by the City to the plaintiff of a sum equal to the aggregate amount allowable by the Workmen’s Compensation Act for the death of her husband. The plaintiff brought this appeal.
The appellant’s contentions are without merit and obviously stem from a fundamental misconception of *637the effect of liability for workmen’s compensation where applicable.
An employer’s liability to his employee for compensation under the Workmen’s Compensation Act for injuries received by the employee in the course of his employment is not a “limited liability” as the appellant mistakenly terms it. It is the whole liability under the parties’ statutory agreement to be bound by the provisions of the Act, and, where such an agreement exists, the injured employee has no other right of action. By virtue of the Compensation Act, an employee’s common law right to damages for injuries suffered in the course of his employment as a result of his employer’s negligence is completely surrendered in exchange for the exclusive statutory right of the employee to compensation for all such injuries, regardless of negligence, and the employer’s liability as a tortfeasor under the law of negligence for injuries to his employee is abrogated: Swartz v. Conradis, 298 Pa. 343, 346, 148 A. 529. In the Swartz case it was said that “When the statutory employer accepts article III [of the Compensation Act] he is relieved of all liability for compensation at common law. Section 303 makes the ‘agreement [referred to in Section 302] operate as a surrender by the parties thereto of their rights to any form or amount of compensation ... or to any method of determination thereof, other than as provided in article III of this act.’ ” See, also, Staggers v. Dunn-Mar Oil & Gas Co., 312 Pa. 269, 274, 167 A. 785. It is plain enough, therefore, that there is no need for a “limited liability” defense or any other defense to a nonexistent right of action.
There is a conclusive presumption under the Workmen’s Compensation Act that the parties to every contract of hiring agree to be bound by the Act unless at the time of the making, renewal or extension of such a contract one or the other of the parties, by express *638statement in writing, rejects tlie provisions of the Act. And, the burden of proving that the Act is not applicable in any given instance is upon the party so asserting: Swartz v. Conradis, supra. Here, the relationship of employer and employee between the City of Philadelphia and the plaintiff’s decedent is admitted and is fully established by the record which also discloses that the employee received his fatal injuries while in the course of his employment by the City. The presumption is therefore conclusive that the provisions of the Workmen’s Compensation Act are applicable, no written rejection of the Act, as the statute specifies, having been offered or even intimated. Indeed, the City is not permitted by law to reject the provisions of the Act. Section 302 (a) of The Workmen’s Compensation Act provides that “It shall not be lawful for any officer or agent of this Commonwealth, or for any county, city, borough, or township therein, or for any officer or agent thereof, or for any other governmental authority created by the laws of this Commonwealth, to give such notice of rejection of the provisions of this article to any employe of the State or of such governmental agency.”
It necessarily follows that the sole procedure available to the plaintiff for the recovery of damages from the employer for her husband’s death from injuries received in the course of his employment was by virtue of the Workmen’s Compensation Act and by that alone.
It so happens, however, just as in the instant case, that an employer may be required to defend his employee’s trespass action for personal injuries received in the course of his employment when the employer is summoned as an additional defendant or is sued jointly with another for such injuries. But, that procedure is for the sole and exclusive purpose of protecting the original or third-party defendant’s right of contribution from the employer and does not ascribe to the em*639ployee or Ms representative a common law right against Ms employer for damages for injuries suffered in the course of his employment. Such was plainly recognized by this court in Maio v. Fahs, 339 Pa. 180, 14 A. 2d 105.
In Maio v. Fahs, supra, the plaintiff was an employee of the additional defendant who had been brought upon the record by the original (third-party) defendant on the allegation that the employer was “severally with him, or alone, liable to the plaintiff for the cause of action declared on in the said suit.” In approving the holding of the court below, Mr. Justice Maxey, speaking for this court, said “though plaintiff [employee] could not issue execution or other process to collect her judgment from [the employer], . . . equitable considerations required the entry of judgment against all the defendants in order- that [the original defendant’s] right to contribution from Ms joint tortfeasor, [the employer], as determined by the jury’s verdict, should not be lost or nullified: [citing cases].”
After judgment had been entered against the defendant employer in Maio v. Fahs, supra, the employer challenged it on the ground that the plaintiff’s exclusive remedy for the wrongful death of her husband, the employee, was under the Workmen’s Compensation Act. While the employer was held to be properly a defendant in the judgment in the employee’s suit because of the original defendant’s right of contribution from the defendant employer, the plaintiff, representing the deceased employee, had no right to collect from the employer on account of the judgment. As to that, this court left no doubt when it said that “It would be repugnant to the letter and spirit of the Workmen’s Compensation Act and would frustrate its purposes to hold that an employer who brings himself within the Act could notwithstanding that fact be held liable to the payment of a judgment obtained by an employee *640against him as an additional defendant and against an original defendant, after both had been adjudged guilty of negligence resulting in the death of that employee.”
The ruling in Maio v. Fahs, supra, was followed and applied in McIntyre v. Strausser, 365 Pa. 507, 76 A. 2d 220, which laid down a further procedural step, namely, that the fact that one of the defendants was the plaintiff’s employer and, consequently, liable for workmen’s compensation was not to be disclosed to the jury at the trial of the negligence action. The rationale of this ruling is obvious upon a moment’s reflection. It would be highly prejudicial to a plaintiff employee in Ms action for damages for negligence for one of the defendants to show that he was liable to the plaintiff for compensation. Such proof would be likely to work to the advantage of the non-employer defendant by way of a reduced verdict.
When the plaintiff in the instant case sought to execute upon the judgment against the City in the trespass action, the City moved promptly to interpose its liability for workmen’s compensation as a bar to the judgment. It is of no moment to the rights of the plaintiff that the City could have moved earlier to have the judgment marked satisfied as to it.
In McIntyre v. Strausser, supra, the plaintiff was an employee of one of the defendants. He received the injuries for which he claimed damages while he was a passenger in his employer’s car which collided with another automobile. The suit was against the employer and the driver of the other vehicle. The employer filed an answer averring that the plaintiff was his employee at the time of the accident and that his only recourse against the employer was under the Workmen’s Compensation Act. The employer was not permitted, however, to introduce any proof at trial of the existence of the employer-employee relationship. A verdict was *641returned in favor of the plaintiff and against the employer, alone, who filed a motion for judgment n.o.v. on the ground that he was liable to the plaintiff for compensation only. The lower court denied the motion, explaining that “It is our opinion that an order should be made refusing the defendant [employer’s] motion for judgment N.O.V., without prejudice, and with the right to file a petition — and obtain a rule on the plaintiff to show cause why the judgment should not be satisfied of record.” On appeal, the late Mr. Justice Stbaene, speaking for a unanimous court, observed that “On motion for judgment n.o.v. by the employer-defendant, which was refused by the court in banc, the court said: ‘Before the trial commenced, and during trial, conferences were held in chambers between counsel and the Trial Judge . . . , who directed that, pursuant to his interpretation of the law expressed in Maio, Exrx., v. Fahs et al., 339 Pa. 180, the claim that plaintiff was an employee of [the one defendant] was not to be disclosed to the jury, and that the case would be tried simply on the evidence that he was a passenger in [the employer’s] car.’ ” The opinion for this court then went on to state that “Since it is clear that the employer-defendant at the trial was properly precluded from establishing the facts concerning the employer-employe relationship, we agree with the learned court below that the proper procedure is for the employer-defendant to rule the plaintiff to show cause why the judgment should not be satisfied of record. See Maio, Exrx., v. Fahs et al., [supra].”
McIntyre v. Strausser plainly teaches that, in an action by an employee against his employer and a third party for damages for injuries due to negligence, the employer-employee relationship is not to be pleaded. As is well known, the intended role of a pleading is to forecast what the pleader hopes to prove at trial, there*642by putting his opponent on notice of what the latter will have to meet; and, thus, the issues are defined: Goodrich-Amram Civil Practice, §1019-1. It would be utterly vain to require a litigant to plead something which, as a matter of law, he will not he permitted to prove or read into evidence at trial. And it would he worse than vain to impale a litigant for not having averred what must not be disclosed to the jnry.
The City waived nothing in respect of the exclusiveness of its liability for workmen’s compensation. It asserted the relationship of employer and employee between it and the plaintiff’s decedent as soon as the plaintiff sought to collect from the City on the judgment in the trespass action. Prior to the entry of judgment against the City, it could not have set np its statutory liability as a bar to the plaintiff’s common-law claim. Nor, when the case went to the jury, could it mention its economic relationship with the defendant: see McIntyre v. Strausser, supra. And, even after verdict, the City could not move for judgment n.o.v. on the ground of the employer-employee relationship. Both the Maio and McIntyre cases, supra, so held. It follows, therefore, that when the City moved to quash the writ of mandamus execution, within a day of its issuance, it acted timely to offset the judgment for which it was not liable in law to the plaintiff. Not possibly can the City he held to have waived a right, which it was not theretofore called upon or permitted to assert, even assuming the right was municipally waivable.
Nor was the employer’s motion to quash the writ of execution in any sense a collateral attack on the judgment, as the appellant erroneously argues. The City has never assailed the validity ox the judgment but merely contends that it imposes no liability on the de*643fendant employer so far as the plaintiff is concerned. When a judgment at law has no standing as an enforceable liability of the one against whom it is entered, the equity powers of the court are called into play to the end that execution on the judgment be denied and that it be marked satisfied. The equitable procedure for relieving against a judgment regular on its face, even out of term time, was fully set out by Mr. Justice Linn in Anstine v. Pennsylvania Railroad Company, 352 Pa. 547, 551, 43 A. 2d 109. While that case was not concerned with the defendant’s freedom from liability to the plaintiff for the judgment at law because of exclusive liability for workmen’s compensation, the principle is nonetheless the same. It was the procedure envisioned in Maio v. Fahs, supra, which, in turn, became the course expressly approved in McIntyre v. Sirausser where we said that “we agree with the learned court below that the proper procedure is for the employer-defendant to rule the plaintiff to show cause why the judgment should not be satisfied of record.”
In the instant case, the learned court below, having assumed to exercise its equitable powers in the premises, conditioned the satisfaction of the judgment on the City’s paying to the plaintiff the aggregate amount of the award she would have received had she proceeded against the City under the provisions of the Pennsylvania Workmen’s Compensation law. That was truly an act of grace. Under advice of her counsel, the plaintiff had refused to enter into an agreement with the City for the payment of the compensation due her, and the year within which such a claim would by law have had to be made has long since past. The action which the learned court below took in this regard was at the instance of the City which has not appealed and stands ready to pay the award.
*644Had the plaintiff based her claim of right to the judgment against the City on the ground that, at the time of her husband’s fatal injury, he was not acting in the course of his employment as an employee of the City (and, consequently, that she was entitled to hold the City as an ordinary tortfeasor), she could have had the pertinent issue of fact duly litigated by directly traversing the City’s averments to the contrary in its petition to quash the writ of mandamus execution and could, thereupon, have had that matter determined at a judicial hearing. Instead of so doing, however, the plaintiff deliberately chose to shun a finding as to the only possible issue of relevant fact and bottomed her claim on the finely spun legal argument, which we have already disposed of, that .the City had waived its statutory freedom from common law liability to its employee for negligence.
Order affirmed.