Fed up with U.S. Supreme Court rulings that have unleashed a torrent of political spending by wealthy mega-donors, local activists have launched an initiative campaign to amend the Constitution to reduce the influence of money on politics.

Initiative 1329 seeks to put Washington on the record as favoring a constitutional amendment that would make it clear “corporations are not persons” and “money is not speech.”

The measure would have no binding authority, but would urge “immediate action” by the state’s congressional delegation to propose such an amendment.

Backers acknowledge I-1329 would be only a small step in the daunting national process required to amend the U.S. Constitution. Such amendments require a two-thirds vote in each house of Congress and ratification by three-quarters of the states.

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But supporters hope grass-roots campaigns will spread to other states, creating the political will necessary for such a change.

“It’s not something we can throw our hands up about,” said former Seattle City Councilmember Jim Street. “If we say it’s hopeless, our political system in generations ahead is going to be dominated by money, not voters.”

Similar initiatives have been approved by big majorities in Montana and Colorado. And legislatures in more than a dozen states have approved resolutions backing the effort, according to United for the People, a national coalition of groups supporting the constitutional amendment.

The Washington effort faces an uphill climb to make this year’s ballot.

I-1329 backers say they’ve gathered about 70,000 signatures to place the measure on the November ballot. To qualify, they need to turn in 246,372 valid signatures by July 3. The campaign now plans to use paid signature gathers to try to reach that mark, but it has struggled to raise money.

The campaign has raised about $33,000 and spent $8,800 of that, according to the state Public Disclosure Commission. The largest donation, of $1,327, came from David Bangs, an investor and former Microsoft manager from Issaquah.

Backers say a wealthy donor has pledged $50,000 toward the signature-gathering effort if the campaign raises an equal amount. The I-1329 campaign declined to reveal the name of the donor, but said his identity will be disclosed to the PDC once the money comes in.

The movement for a constitutional amendment is part of a national backlash against the Supreme Court’s 2010 Citizens United ruling and related decisions striking down various limits on campaign spending, declaring such restrictions violations of free-speech rights.

Those rulings have helped unleash unprecedented amounts of independent spending in political races, much of it through super PACs, which can raise unlimited sums of money.

During the 2012 election cycle, such spending tripled compared with 2008 and topped $1 billion for the first time, according to the Center for Responsive Politics.

The mega-rich have accounted for much of that explosion. In 2012, the donations of 1.4 million Americans in the presidential race were matched by 61 big donors who gave $285 million to super PACs, according to an analysis by liberal advocacy groups U.S. PIRG and Demos.

Much of the outcry against Citizens United has come from Democrats and liberal organizations. Initiative 1329 campaign manager Libby Carr acknowledged the campaign has yet to receive endorsements from Republican or conservative groups, but added “we are looking for them.”

A spokesman for a national group that supported the Citizens United decision said the proposed constitutional amendment backed by I-1329 is worrisome.

“Free speech is free speech,” said Joe Trotter, a spokesman for the Center for Competitive Politics, a nonprofit that fights campaign-finance regulations. “Once you limit the rich, what is to prevent everyone else from being restricted?”

The last amendment to the U.S. Constitution, the 27th, which restricted the power of Congress to raise its own pay, was ratified in 1992, more than 200 years after the first state approved it.

Jim Brunner: 206-515-5628 or jbrunner@seattletimes.com. On Twitter @Jim_Brunner