OPINION
O’BRIEN, Justice.This matter is before us on a petition for a writ of prohibition filed by Philadelphia Police Officers Gerald Salerno, Charles Gubler, Steven Maggiancaldo, Andrew Yalet*62sko, Howard Davis, James Dorwart, David Ridgeway, Sid Mullins and Robert Butler.1
On July 2, 1977, Jose Reyes was shot to death in Philadelphia. Police Officer Gerald Salerno was alleged to be the person who shot Reyes. The Philadelphia District Attorney’s office, through its homicide division, began an investigation into the circumstances of the Reyes-Salerno shooting.
On August 3, 1977, five of the above-mentioned police officers were requested to appear at the office of the chief of the homicide division. On advice of counsel, the five officers appeared, but refused to make any statements concerning the facts surrounding the Reyes-Salerno shooting.
On August 5, 1977, the district attorney’s office filed a petition with Judge Mema B. Marshall of the Court of Common Pleas of Philadelphia. The gravamen of the petition alleged that the Philadelphia District Attorney, pursuant to § 8-409 of the Philadelphia Home Rule Charter, had investigative subpoena power. Pursuant to § 8-409 of the charter, the district attorney asked the court to confirm such subpoena power. On August 18, 1977, the court, per Judge Marshall, issued an order:
“ . . . [T]hat the District Attorney of Philadelphia may subpoena the following police officers to appear and give testimony and other evidence regarding the fatal shooting of Jose Reyes.” (Emphasis added.)
On August 23, 1977, the petitioners filed a petition for a writ of prohibition in this court. On August 29, 1977, a justice of this court issued a stay of the proceeding pending disposition of the petition for writ of prohibition by the full court. On September 14, 1977, this court granted a rule to show cause, returnable on October 17, 1977. On that date, the petition was argued before the full court.
*63The initial inquiry is whether a writ of prohibition is the proper remedy in the instant case.
In Carpentertown Coal & Coke Co. v. Laird, 360 Pa. 94, 102, 61 A.2d 426, 430 (1948), this court stated:
“ . . The writ of prohibition is one which, like all other prerogative writs, is to be used only with great caution and forbearance and as an extraordinary remedy in cases of extreme necessity, to secure order and regularity in judicial proceedings if none of the ordinary remedies provided by law is applicable or adequate to afford relief. It is a writ which is not of absolute right but rests largely in the sound discretion of the court. It will never be granted where there is a complete and effective remedy by appeal, certiorari, writ of error, injunction, or otherwise: see First Congressional District Election, 295 Pa. 1, 13, 144 A. 735, 739, 740, and cases referred to in the dissenting opinion in Philadelphia County Grand Jury Investigation Case, 347 Pa. 316, 330-334, 32 A.2d 199, 206-208; also Roche, U. S. District Judge v. Evaporated Milk Association, 319 U.S. 21, 26, 63 S.Ct. 938, 87 L.Ed. 1185; United States Alkali Export Association, Inc. v. United States, 325 U.S. 196, 65 S.Ct. 1120, 89 L.Ed. 1554. As pointed out in the last cited authority, 325 U.S. at page 203, 65 S.Ct. at page 1125, ‘appellate courts are reluctant to interfere with decisions of lower courts, even on jurisdictional questions, which they are competent to decide and which are reviewable in the regular course of appeal. . The [extraordinary] writs may not be used as a substitute for an authorized appeal.’ ”
In Commonwealth v. Mellon Nat. Bk. & Tr: Co., 360 Pa. 103, 107, 108, 61 A.2d 430, 433 (1948), this court further defined the scope and availability of a Writ of Prohibition:
“Ferris in Extraordinary Legal Remedies (p. 439 et seq.) said: ‘It is well settled that a writ of prohibition may not be used to usurp or perform the functions of an appeal, writ of error or certiorari, or to correct any mistakes, errors or irregularities in deciding any question of law or fact within its jurisdiction. The office of the writ, as at *64common law, is to prevent an unlawful assumption of jurisdiction, not to correct mere errors and irregularities in matters over which the court has cognizance. Where the general scope and purpose of the action is within the jurisdiction of the court, any error or overstepping of its authority in a portion of its judgment, or any other error in its proceedings, is only ground for a review or appeal, and not prohibition. That is to say, where there is authority to do the act, but the manner of doing it is improper, the writ will not lie. In other words, whatever power is conferred may be exercised, and, if it be exercised injudiciously, erroneously or irregularly, it amounts to error merely and not to a usurpation or excess of jurisdiction. In such a case, however gross the error, irregularity or mistake, the writ does not lie, not because, as is sometimes erroneously or irregularly, it amounts to error merely or such remedies are inhibited, but for the reason that there has been no usurpation or abuse of power.’ (Emphasis added.)
“The American and English Encyclopaedia of Law (2d Ed.), Vol. 23 at p. 200 sums up the law applicable to writs of prohibition as follows: ‘Where the inferior court has jurisdiction of the matter in controversy, prohibition will not lie. The writ does not lie to prevent a subordinate court from deciding erroneously or from enforcing an erroneous judgment in a case in which it has a right to adjudicate, and it matters not whether the court below has decided correctly or erroneously; its jurisdiction of the matter in controversy being conceded, prohibition will not lie to prevent an erroneous exercise of that jurisdiction. The exercise of power which it is sought to prohibit must be wholly unauthorized by law. Mere errors or irregularities in the proceedings which do not go to the jurisdiction . of the inferior court to take the proposed action, and the merits of the action will not be considered.’ To the same effect is 50 Corpus Juris, sec. 3, p. 655.” (Footnote omitted.)
*65In Com. ex rel. Specter v. Shiomos, 457 Pa. 104, 107-108, 320 A.2d 134, 136 (1974), this court synthesized the Carpentertown and Mellon Bank rationales by saying:
“ . . . Thus, under Carpentertown, a two-pronged test was set forth for this Court to follow when considering the granting of a Writ. The first aspect of the test is whether adequate remedies are provided at law to afford relief. .
“The second prong of the test is whether there is extreme necessity for the relief requested to secure order and regularity in judicial proceedings. . . . ”
A. Adequate remedy at law.
In the instant case, the court below issued an order authorizing the district attorney to issue subpoenas to nine Philadelphia Police Officers in connection with that office’s homicide investigation of possible criminal culpability in the Reyes shooting. The authority proffered by the district attorney for his authority to issue investigative subpoenas was § 8-409 of the Philadelphia Home Rule Charter. Section 8-409 provides:
“Every officer, department, board or commission authorized to hold hearings or conduct investigations shall have power to compel the attendance of witnesses and the production of documents and other evidence and for that purpose it may issue subpoenas requiring the attendance of persons and the production of documents and cause them to be served in any part of the City. If any witness shall refuse to testify as to any fact within his knowledge or to produce any documents within his possession or under his control, the facts relating to such refusal shall forthwith be reported to any one of the Courts of Common Pleas of Philadelphia County and all questions arising upon such refusal and also upon any new evidence not included in the report, which new evidence may be offered either in behalf of or against such witness, shall as promptly as possible be heard by such court. If the court shall determine that the testimony or document required *66of such witness is legally competent and ought to be given or produced by him, the court may make an order commanding such witness to testify or to produce documents or do both and if the witness shall thereafter refuse so to testify or so to produce documents in disobedience of such order of the court, the court may deal with the witness as in other cases.”
No subpoenas pursuant to § 8-409 have been issued by the district attorney to the petitioners. The record, however, is clear that none of the police officers intends to comply with the district attorney’s subpoenas. Petitioners contend that the district attorney’s office is not within the phrase: “Every officer, department, board or commissioner authorized to hold or conduct investigations” of § 8-409, and, therefore, the district attorney has no authority to issue subpoenas. This argument, however, goes not to the authority of the Court of Common Pleas to compel compliance, but rather is a statutory construction argument cognizable on appeal.
In Cathcart v. Crumlish, 410 Pa. 253, 254-55, 189 A.2d 243, (1963), this court determined that an adequate remedy at law existed to challenge the district attorney’s alleged subpoena authority under § 8-409 of the Philadelphia Home Rule Charter and, therefore, the court vacated an equity decree which dismissed a bill in equity seeking to enjoin the issuance of the subpoena. The court, in Cathcart, summarized the pertinent facts as follows.
“In pursuance of an investigation he was conducting, the district attorney of Philadelphia issued subpoenas commanding appellants to appear at his office on November 27, 1961 to testify on certain matters then under investigation. These subpoenas were issued on the alleged authority of section 8-409 of the Philadelphia Home Rule Charter. Appellants filed complaints in equity on November 22, 1961, seeking to enjoin the district attorney from requiring them to appear and testify. After hearing argument, the lower court dismissed appellants’ complaint, holding, inter alia, that section 8-409 of the Philadelphia *67Home Rule Charter empowered the district attorney to issue subpoenas. An appeal to this Court was then taken.”
The court, in Cathcart, at pages 255-57, 189 A.2d at page 244, went on and stated:
“ . . . since section 8-409 of the Philadelphia Home Rule Charter prescribes a specific statutory procedure wherein the validity of subpoena issued under this section may be tested. See Stahl, Attorney General v. Insurance Company of North America, 408 Pa. 483, 486, 184 A.2d 568 (1962). This section provides for the district attorney to report any non-compliance to a common pleas court which shall promptly hear arguments on the validity of the subpoena. Under the Act of March 21, 1806, P.L. 558, 4 Sm.L. 326, 46 P.S. § 156, it has long been held in various contexts that where a remedy or method of procedure is provided by an act, those procedures should be followed exclusively. See, e. g., Knup v. Philadelphia, 386 Pa. 350, 126 A.2d 399 (1956). Applying this principle .to the case before us, we conclude that appellants cannot question the validity of the subpoena until they are called before the common pleas court.” (Footnotes omitted.)
******
“ . . . The remedy is adequate since appellants will suffer no irreparable harm, or for that matter any harm at all, if they have to wait until the district attorney invokes the enforcement procedures before they can contest the subpoena. . . . ”
Moreover, no petition for enforcement of the administrative subpoena has been filed pursuant to § 8-409 of the Philadelphia Home Rule Charter. Rather, the district attorney has sought a “confirmation” of authority under the Charter provisions to issue the subpoena.
In Pa. Crime Commission Subpoena, 453 Pa. 513, 516-518, 309 A.2d 401, 404 (1973), this court, in a similar situation of dealing with administrative subpoenas, stated:
“Preliminarily, we note that appellants’ motion to quash the subpoena in the Common Pleas Court was improper. *68Appellants cannot contest the validity of the subpoena until the Commission invokes enforcement procedures in either the Courts of Common Pleas or the Commonwealth Court. This is so because, unlike a judicial subpoena, the Crime Commission is not given power to enforce compliance. Therefore, individuals are not placed in the dilemma of having to disobey the Commission’s subpoena at their peril in order to contest its validity. Failure to comply is not punishable by fine or imprisonment unless it continues after a court has ordered compliance. See Cathcart v. Crumlish, 410 Pa. 253, 189 A.2d 243 (1963); Alpha Club of West Philadelphia v. Pennsylvania Liquor Control Board, 363 Pa. 53, 68 A.2d 730 (1949). (Footnote omitted.) * * * * * *
“Until the Commission invokes the aid of a court to enforce compliance with its subpoenas, the court is without jurisdiction in the matter. To hold otherwise would be to ignore the obvious possibility that the Commission may elect not to enforce its subpoenas. Until the decision is made by the Commission to seek enforcement the subpoena is no more than an invitation to appear which can be ignored without peril by the recipient. Therefore, the premature initiation of equitable proceedings by the appellants is in effect a nullity and it is incapable of divesting the Commission of its legal right to elect to proceed to seek enforcement in the forum of its choice as provided under the statutes.” (Footnote omitted.)
Cathcart, supra, established that § 8-409 of the Philadelphia Home Rule Charter provides an adequate remedy at law to challenge the district attorney’s subpoena power. An adequate remedy at law existing, a writ of prohibition is not available. See Pa. Crime Commission Subpoena, supra.
Moreover, petitioners’ argument does not go to the subject matter jurisdiction of the Court of Common Pleas to entertain the petition; rather it goes to whether the district attorney is a member of the class of city officers within the enumeration of § 8-409. To issue a writ of prohibition in the instant case would require its issuance every time a *69party objected to the opposing side’s statutory standing or common-law authority for certain action.
B. Necessity for the relief requested in order to secure order and regularity in the judicial proceedings.
The second prong of the Shiomos test requires that the granting of the writ of prohibition “secure order and regularity in judicial proceedings.” See Shiomos, supra, 457 Pa. at 108, 320 A.2d at 136.
In the instant case, the granting of the writ would seem to defeat rather than further order and regularity of judicial proceedings. No subpoenas have been issued pursuant to the order of the court below. While the record indicates that the police officers, if subpoenaed, would not comply, the record does not show whether such noncompliance would be based on a valid exercise of the officers’ constitutional rights against self-incrimination.
The Court, in Cathcart, supra, 410 Pa. at 256-57, 189 A.2d at 245, stated:
“. . . The remedy is adequate since appellants will suffer no irreparable harm, or for that matter any harm at all, if they have to wait until the district attorney invokes the enforcement procedures before they can contest the subpoena. Unlike a judicial subpoena, public officers who are allegedly vested with subpoena power under section 8 — 409 are not given the power to enforce compliance. Disobedience is not punishable by imprisonment or fine unless it continues after a court has ordered compliance. See Annotation to § 8-409, Philadelphia Home Rule Charter. Therefore, appellants are not placed in the unfortunate dilemma of having to disobey the district attorney’s subpoena at their peril in order to contest their validity.”
Cathcart makes clear that the petitioners need not be held in contempt to challenge the district attorney’s authority under the Philadelphia Home Rule Charter. Petitioners can raise any challenges or possible defense to the subpoena at the *70time the petition to enforce is filed. See Pa. Crime Commission Subpoena, supra.
In Com. ex rel. Specter v. Freed, 424 Pa. 508, 228 A.2d 382 (1967), the Philadelphia district attorney subpoenaed M. Philip Freed, a magistrate. The district attorney’s theory for his authority to issue a subpoena was the same as this case, § 8-409 of the charter. A plurality opinion (Justice Roberts, joined by Justices Jones and O’Brien) stated that § 8-409 of the charter did not grant subpoena power. Justice Cohen filed a concurring opinion in which he reached the same result but specifically refused to address the charter issue. Justice Eagen, now Chief Justice, filed a concurring opinion, joining the result reached but again not ruling on the charter issue. C. J. Bell dissented. Specter is instructive in the instant case, not for its discussion of the merits of the district attorney’s subpoena power under the charter but rather for its procedural posture. In Specter, the district attorney issued the subpoena and upon Freed’s failure to comply, the district attorney went into Common Pleas Court to enforce the subpoena. Common Pleas Court agreed with the district attorney and ordered compliance. Freed appealed from that order to this court. Specter does not control the instant case. Initially Specter is a plurality opinion by three members of the court and, therefore, it is not binding precedent. Moreover, in Specter, the proper procedure was used. An appeal was taken after a compliance order. All that we decide today is that a writ of prohibition is not the proper procedure or remedy to challenge the district attorney’s alleged subpoena power under § 8-409 of the Philadelphia charter.
Under the facts of the instant case, i.e. no subpoenas having been issued, and no petition to enforce subpoenas having been filed, we are of the opinion that the second prong of the Shiomos test has not been met. Writ of prohibition is denied.
The district attorney, in his brief, requests that this court take plenary jurisdiction pursuant to § 205 of the Appellate Court Jurisdiction Act, Act of July 31, 1970, P.L. *71673, No. 223, art. II, § 205, 17 P.S. § 211.205 (Supp.1977). The request for plenary jurisdiction is denied.
Petition for writ of prohibition is denied and the district attorney’s request for assumption of plenary jurisdiction is denied.
EAGEN, C. J., and NIX and MANDERINO, JJ., concur in the result. PACKEL, J., files a dissenting opinion.. § 201 of the Appellate Court Jurisdiction Act of 1970, Act of July 31, 1970, P.L. 673, No. 223, art. II, § 201, 17 P.S. § 211.201 provides in relevant part:
“The Supreme Court shall have original but not exclusive jurisdiction of . . . (2) all cases of mandamus or prohibition to courts of inferior jurisdiction . . ..”