Opinion by
Mb. Justice Jones,In this appeal we are confronted basically with the same factual situation and legal principles presented to this Court in Crosson v. Downingtown Area School District, 440 Pa. 468, 270 A. 2d 377 (1970).
Appellants, taxpayers, in the Court of Common Pleas of Chester County in an equity action sought to enjoin a school district1 and its tax collectors from collecting occupation taxes and to have the taxes declared invalid and unconstitutional. The occupational classification and assessment schedule is identical to that in Crosson although the tax resolution is different as to both the exemptions as well as the rate of taxation.2 Again, as in Crosson, the authority for the school district’s action was The Local Tax Enabling Act, Act of December 31, 1965, P. L. 1257, §1 et seq., 53 P.S. §6901 et seq. (Supp. 1970).
The same collateral issues raised in Crosson concerning the occupational assessments made by the county assessing authorities upon which the tax was levied were raised below in the case at bar. An additional collateral argument was raised that, although each type of occupation was valued by the chief county assessor prior to the resolution, the occupation of each individual taxpayer situated within the school district was not *499pigeon-holed within the aforementioned occupational schedule until after the resolution was adopted. Hence, the argument is made that the county assessment at the time of the levy was improper and incomplete.
While a direct challenge to the tax resolution, comparable to that in Crosson, was advanced to the effect that the tax was not assessed and levied within the time provided by statute, two novel contentions were asserted: (1) the tax violates the Uniformity Clause of the Pennsylvania Constitution, Article VXII, §1, as it was the averred policy of the school district to create a de facto exemption for persons under twenty-one or over sixty-five or earning less than f600 per year, even though such exemptions were not included in the resolution; and (2) the schedule of occupational classification incorporated into the tax resolution is so vague and indefinite as to be unconstitutional.
The chancellor, by an adjudication dated June 2, 1969, entered a decree nisi dismissing the complaints, exceptions to this decree were dismissed by the court en banc and a final decree was entered on October 20, 1969. This appeal followed.
Turning to the collateral issues concerning the allegedly improper assessment procedures, appellee argued and the chancellor and the court en banc agreed, that a court of equity does not have jurisdiction or competency to determine the controversy. As to this contention we could simply affirm on the basis of Crosson. However, since the proper jurisdiction of equity in tax disputes has recently been expanded as well as contracted in a trilogy of cases, perhaps a more thorough explanation of this development is in order. The first of these cases, Lynch v. Owen J. Roberts Sch. Dist., 430 Pa. 461, 244 A. 2d 1 (1968), considered the earlier case law in this area and concluded that, when a constitutional challenge to a tax resolution is pre*500seated, equity has the jurisdiction and competency to consider both the constitutional and nonconstitutional challenges even though there exists a specific statutory remedy at law. Moreover, Lynch demonstrated that, once equity obtains jurisdiction by reason of the presence of the constitutional issue, it may invalidate the tax resolution on solely nonconstitutional grounds without ever considering the constitutional argument. Rochester & Pittsburgh Coal Co. v. Indiana County Board of Assessment and Revision of Taxes, 438 Pa. 506, 266 A. 2d 78 (1970), actually restricted the broad doctrine of Lynch by requiring that the constitutional challenge affording jurisdiction to a court of equity must be “a substantial question of constitutionality (and not a mere allegation).” 438 Pa. at 508, 266 A. 2d at 79. Finally, Crosson limited Lynch by holding that, even the presence of a substantial question of constitutionality concerning the tax resolution, does not justify equity taking jurisdiction over every collateral, nonconstitutional attack on the assessment. The thrust of Crosson is that, if the nonconstitutional challenge to the assessment could not have been maintained in a separate action in equity on the assessment, it cannot be advanced in an attack on the tax resolution which was based on the assessment. As in Crosson, appellants’ instant contentions in this regard do not substantially question either the constitutionality of the assessment or that the Chief County Assessor lacked the power to make the assessments and, in addition, a statutory appeals route is available.3 Accordingly, a court of equity should not entertain these collateral attacks.
*501Appellants’ argument that the tax was not assessed (computed) within the time provided by statute4 was also considered in Crosson, which held the statutory time limit to be directory and not mandatory. 440 Pa. at 477-78, 270 A. 2d at 381-82. Crosson’s holding renders further discussion of this point unnecessary.
In the court below appellants contended that, while the tax resolution contained no exemptions, it was the policy of the school district in the enforcement of the resolution to exclude persons under twenty-one or over sixty-five or earning less than $600 per year and that these de facto exemptions violated the Uniformity Clause of our Constitution and should be enjoined. In Saulsbury v. Bethlehem, Steel Co., 413 Pa. 316, 196 A. 2d 664 (1964), we found an occupational privilege tax imposed solely on persons earning $600 or more violated the uniformity requirements. On the other hand, Grosson concluded that a tax classification excluding those under twenty-one from payment of an occupation tax did not violate the Uniformity Clause.
We have never decided the substantial constitutional question of whether persons over sixty-five may be released from liability from taxation nor do we need to decide it now. Even if the classification of those over sixty-five years were found to be unconstitutional as was the $600 exemption in Saulsbury, appellants have failed to prove the existence of such a policy or practice. Our case law involving the constitutionality of state taxation places a very heavy burden on those who seek to upset such taxation. Prichard v. Willistown Township Sch. Dist., 394 Pa. 489, 147 A. 2d 380 (1959) (not invalid unless “clear, palpable and plain violation”) ; L. J. W. Realty Corp. v. Philadelphia, 390 Pa. 197, 134 A. 2d 878 (1957) (“clearly, palpably, plain *502ly,” leaving “no doubt or hesitation in our minds”); Sablosky v. Messner, 372 Pa. 47, 92 A. 2d 411 (1952). We ascertain no reason to apply a different test in determining the validity of local municipal taxation. The record before us discloses that only one of twenty assessors testified that she excluded anyone—those under twenty-one only—another witness testified that the instruction complained of was given and eight other assessors did not state whether there was any such policy. Other evidence in this vein was without substance. The chancellor and the court en banc made no finding of fact that any such exclusionary instruction was given and our scrutiny of the record convinces us no failure to so find was justified by the evidence of record. Appellants have failed to discharge the heavy burden placed on them.
The occupational classification incorporated into the tax resolution is identical to the one considered in Orosson and Orosson controls the disposition of appellants’ final argument that the classification is so vague and indefinite as to be unconstitutional.
Decree affirmed. Appellants pay costs.
Mr. Justice Cohen, Mr. Justice Eagen and Mr. Justice Pomeroy concur in the result.Here we deal with a second-class, rather than Crosson’s third-class, school district.
“Now, Therefore, be it resolved by the Board of School Directors of the CoatesviUe Area School District, in pursuance of the authority granted by The Local Tax Enabling Act (Act 511 of 1965), as amended, (53 P.S. 6901) :
“Section 1. An occupation tax of 250 mills on occupations as assessed for the school year beginning on July 1, 1968 and ending on June 30, 1969, upon the occupations of all persons residing in the Coatesville Area School District, Chester County, Pennsylvania, made taxable by the laws of the Commonwealth of Pennsylvania, as determined by the Chief Assessor of the County of Chester.”
The Fourth to Eighth Class County Assessment Law, Act of May 21, 1948, P. L. 571, art. VII, §§701-704, as amended, 72 P.S, §§5453.701-5453.704
Act of March 10, 1949, P. L. 30, art. VI, §672a, 24 P.S. §6-672a.