WASHINGTON (AP) — The Supreme Court on Monday turned away a plea to revisit its 2-year-old campaign finance decision in the Citizens United case and instead struck down a Montana law limiting corporate campaign spending.

The same five conservative justices in the Citizens United majority that freed corporations and labor unions to spend unlimited amounts in federal elections joined Monday to reverse a Montana court ruling upholding the state's century-old law. The four liberal justices dissented.

"The question presented in this case is whether the holding of Citizens United applies to the Montana state law. There can be no serious doubt that it does," the court said in an unsigned opinion.

The Citizens United decision paved the way for unlimited spending by corporations and labor unions in elections for Congress and the president, as long as the dollars are independent of the campaigns they are intended to help. The decision, grounded in the freedom of speech, appeared to apply equally to state contests.

But Montana aggressively defended its 1912 law against a challenge from corporations seeking to be free of spending limits, and the state Supreme Court sided with the state. The state court said a history of corruption showed the need for the limits, even as Justice Anthony Kennedy declared in his Citizens United opinion that independent expenditures by corporations "do not give rise to corruption or the appearance of corruption."

In a brief dissent Monday, Justice Stephen Breyer said campaign spending since 2010 "casts grave doubt on the court's supposition that independent expenditures do not corrupt or appear to do so."

Twenty-two states and the District of Columbia, as well as Sen. John McCain and other congressional champions of stricter regulations on campaign money, joined with Montana.

New York Attorney General Eric Schneiderman said Monday's "decision gives short shrift to states' vital interests in protecting their democratic processes and institutions from the threats posed by unlimited corporate spending in campaigns."

James Bopp, the lawyer who challenged the Montana law, said," This closes the door on the argument that unique facts in a certain state can be employed to overturn Citizens United."

In February, Breyer and Justice Ruth Bader Ginsburg, both dissenters in Citizens United, challenged Kennedy's view that the independent campaign spending could not be corrupting by virtue of the absence of links to a campaign.

When the court blocked the Montana ruling in February, Ginsburg issued a brief statement for herself and Breyer saying that campaign spending since the decision makes "it exceedingly difficult to maintain that independent expenditures by corporations 'do not give rise to corruption or the appearance of corruption.'"

Ginsburg appeared to be referring to the rise of unregulated super PACs that have injected millions of dollars into the presidential and other campaigns. She said the case "will give the court an opportunity to consider whether, in light of the huge sums currently deployed to buy candidates' allegiance, Citizens United should continue to hold sway."

The corporations that sued over the law said it could not remain on the books after the Citizens United decision.

Montana urged the high court to reject the appeal, or hold arguments. The state would have preferred either of those outcomes to what the court did Monday — that is, issue what the court calls a summary reversal without holding new oral arguments. The prevailing side in the lower court almost always strives to avoid high court review. But Montana and its supporters hoped a thorough debate over the Citizens United decision would lead to its reconsideration or at least limits on its reach.

The case is American Tradition Partnership v. Bullock, 11-1179.