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.”