[4] Then-Governor Tom Judge called the statute "the most significant piece of legislation enacted in Montana in this century.

[8] Coal producers in Montana and 11 out-of-state utilities (including Commonwealth Edison) challenged the constitutionality of the severance tax, arguing it was invalid under the Commerce and Supremacy Clauses of the U.S.

Additional Midwestern utilities joined the suit, claiming that the state of Montana was acting like OPEC and accusing Montanans of being "blue-eyed Arabs".

[30] Justice Marshall next identified how the fourth prong of the Complete Auto test should be interpreted: The relevant inquiry under the fourth prong of the Complete Auto Transit test is not, as appellants suggest, the amount of the tax or the value of the benefits allegedly bestowed as measured by the costs the State incurs on account of the taxpayer's activities.

Beyond that threshold requirement, the fourth prong of the Complete Auto Transit test imposes the additional limitation that the measure of the tax must be reasonably related to the extent of the contact, since it is the activities or presence of the taxpayer in the State that may properly be made to bear a "just share of state tax burden," Western Live Stock v. Bureau of Revenue, 303 U.S., at 254.

[38] Appellants had also argued that the Montana tax "frustrated" the broad goals of national energy policy, but the Court refused to agree on two grounds.

First, the Court would not overturn a state act unless "the nature of the regulated subject matter permits no other conclusion, or that the Congress has unmistakably so ordained."

[39] Second, the Supreme Court found that during debates over recent national energy legislation Congress had been fully cognizant of the Montana tax and had refused to take action to pre-empt it or ameliorate its impact on other states.

"[46] Blackmun characterized the majority's decision as "mechanical," and claimed it was not in step with prior Court rulings on burdensome taxation.

[48] Accordingly, given the economic conditions and importance of national energy policy, Blackmun would have remanded the case for trial for further determination of these issues.

In Montanans for the Coal Trust v. State, the Montana Supreme Court agreed and enjoined the licensing law.

[2] The Crow Tribe sued, claiming that the Montana tax impinged on their tribal sovereignty and was pre-empted by federal law.

[2][53] Commonwealth Edison Co. v. Montana has been criticized by legal scholars for overturning Heisler v. Thomas Colliery Co. and subsequent rulings.

[54] Other legal scholars criticize the ruling for, in their view, undermining the importance of the fourth prong of the Complete Auto Transit test.