Twenty-two states and the District of Columbia are backing Montana in its fight to prevent the US supreme court's 2010 Citizens United decision from being used to strike down laws restricting corporate spending in political campaigns.

The states led by New York are asking the high court to preserve Montana's state-level regulations on corporate expenditures, according to a copy of a brief written by New York's attorney general's office and obtained by the Associated Press. The brief will be publicly released on Monday.

The supreme court is being asked to reverse a state court's decision to uphold the Montana law. Virginia-based American Tradition Partnership is asking the nation's high court to rule without a hearing because the group says the state law conflicts directly with the Citizens United decision that removed the federal ban on corporate campaign spending.

The supreme court has blocked the Montana law until it can look at the case.

The Montana case has prompted critics to hope the court will reverse itself on the controversial Citizens United ruling. The 22 states and DC say the Montana law is sharply different from the federal issues in the Citizens United case, so the ruling shouldn't apply to Montana's or other state laws regulating corporate campaign spending.

But the states also said they would support a supreme court decision to reconsider portions of the Citizens United ruling either in a future case or in the Montana case, if the justices decide to take it on.

Legal observers say don't count on the supreme court reconsidering its decision.

"It is highly unlikely that the court would reverse its decision in Citizens United," said law professor Richard Hasen of the University of California-Irvine.

At best, the court would listen to arguments and might agree a clarification is needed to allow the Montana law to stand. But even that is a long shot, Hasen said.

Montana attorney-general Steve Bullock argues that political corruption in the Copper King era led to the state ban on corporate campaign spending. A clarification of Citizens United is needed to make clear that states can block certain political spending in the interest of limiting corruption, he said.

American Tradition Partnership argues that the state bans unfairly restrict the ability of corporations to engage in the political process that also affects them.

Bullock wrote in a brief to be released Monday that the state does not "ban" corporate political speech, rather, it regulates that speech by requiring the formation of political action committees.

The Democrat, who is running for governor, said the upstart political corporations hoping to take advantage of unfettered spending are merely "an anonymous conduit of unaccountable campaign spending."

Montana and the other states are asking the court to either let the Montana supreme court decision stand or to hold a full hearing. They argue laws like the one in Montana that bans political spending straight from corporate treasuries are needed to prevent corruption.

The other states, many with their own type of restrictions hanging in the balance, argue local restrictions are far different than the federal ban the court decided unconstitutionally restricted free speech. Further, state elections are at much greater risk than federal elections of being dominated by corporate money, requiring tailored regulation, the states' court filing says.

"The federal law struck down in Citizens United applied only to elections for President and US Congress," New York attorney-general Eric Schneiderman wrote on behalf of the states. "By contrast, Montana's law applies to a wide range of state and local offices, including judgeships and law enforcement positions such as sheriff and county prosecutor."

The joining states, unlike Montana, ask the court to go further and reconsider core findings in Citizens United. They argue, for instance, it was wrong for the court to say unlimited independent expenditures rarely cause corruption or the appearance of corruption.

And other critics of the Citizens United decision who believe the court was wrong to grant corporations constitutional rights, have intervened and asked the court to reverse itself.

"There is a growing bipartisan consensus that Citizens United needs to be overturned, and Montana is leading the way," said Peter Schurman, spokesman for a group called Free Speech For People. "The supreme court has an opportunity to revisit Citizens United here. That is important because there is evidence everywhere that unlimited spending in our elections creates both corruption and the appearance for corruption."

On Friday, Montana's case was given a boost when US senator John McCain and Sheldon Whitehouse signed on in support. The senators argue evidence following the Citizens United decision, where millions in unregulated money has poured into presidential elections, shows that large independent expenditures can lead to corruption.

The states who filed the brief in support of Montana are New York, Arkansas, California, Connecticut, Delaware, Hawaii, Idaho, Illinois, Iowa, Kentucky, Maryland, Massachusetts, Minnesota, Mississippi, Nevada, New Mexico, North Carolina, Rhode Island, Utah, Vermont, Washington, West Virginia and the District of Columbia.