Just shy of two years after the Supreme Court’s Citizens United ruling, a Montana legal challenge has set the stage for the high court to revisit its landmark decision to deregulate corporate political spending.

The Montana Supreme Court last week rejected a constitutional challenge to the state’s century-old prohibition on independent corporate campaign expenditures. That Montana statute was technically nullified when the U.S. Supreme Court threw out federal limits on independent corporate and union political spending in 2010.

But unlike officials in many states with election laws upended by the ruling, who took steps to repeal or amend those statutes, Montana officials rose to their state law’s defense. Montana Attorney General Steve Bullock went so far as to testify on Capitol Hill that the state’s 1912 Corrupt Practices Act “is a system Montanans continue to believe in,” effectively inviting a legal challenge.

Three Montana corporations took him up on it, arguing in Western Tradition Partnership v. Montana that the state law flies in the face of Citizens United v. Federal Election Commission and violates the First Amendment. A lower court agreed, but on Friday the state Supreme Court reversed that ruling, 5-2.

Writing for the majority, Chief Justice Mike McGrath concluded that Montana’s sparse population, dependence on the mining and agricultural industries, and history of corruption make the state “especially vulnerable to continued efforts of corporate control to the detriment of democracy and the republican form of government.”

Activists working to overturn the Citizens United ruling hailed the Montana ruling as a win-win. The high court will have little choice but to take up the case, predicted John Bonifaz, co-founder and director of the group Free Speech for People, because otherwise virtually any other state could follow Montana’s lead. Before the Citizens United ruling, two dozen states restricted corporate campaign spending in one form or another.

Were the high court to let the Montana Supreme Court ruling stand, Bonifaz said, “there would be enormous pressure on those states to now start enforcing their laws or reinstating their laws.” Conversely, if the Supreme Court reverses the Montana high court, he argued, his group’s mission to overturn Citizens United through a constitutional amendment would receive an important boost.

“That kind of ruling would even more clearly demonstrate why a constitutional amendment is necessary to overturn the [Citizens United] ruling,” he said.

The Montana ruling gives the Supreme Court justices who voted with the majority in Citizens United the opportunity to “beat a tactical retreat,” election lawyer Trevor Potter said, in the wake of the public outcry and campaign finance controversies that the ruling triggered.

The court deregulated corporate spending on the grounds that the money would be fully disclosed and spent independently from candidates, Potter said, but he argued that neither has turned out to be the case.

“Things have not turned out the way the court majority predicted they would,” said Potter, a former Federal Election Commission chairman who heads the Campaign Legal Center, which advised Montana officials on the case. The court would be unlikely to reverse Citizens United outright but may rule that special circumstances such as Montana’s give states certain latitude.

But First Amendment advocates scoff at the notion that anyone on the high court would now regard Citizens United in a different light.

“There’s no evidence that any of these judges really think that they made a mistake,” said Brad Smith, another former FEC chairman who heads the Center for Competitive Politics. The Citizens United ruling was a “pro-free speech, pro-democracy decision” that has enhanced political competition and participation, Smith added. He predicted that the Supreme Court will reverse the Montana ruling summarily, without argument.

On one point, however, Smith agreed with Citizens United’s detractors: The high court will not simply let the Montana decision stand, he maintained.

“If the Montana decision were allowed to stand, it essentially would completely overrule Citizens United, because effectively, every state could make that [same] claim,” Smith said. Assuming that the Montana ruling is appealed, as predicted, the Supreme Court could face the question of whether to revisit Citizens United as early as this spring.