Last year, Hawaii tried — and failed — to impose a 1 percent tax on nonprofit groups. Boston has asked nonprofits to pay the city what is essentially a discounted property tax, and Chicago plans to ask nonprofits to start paying water and sewer fees.

Not surprisingly, such plans run into stiff opposition from nonprofit groups and their political supporters. But in California, the rules on the property tax exemption for nonprofits evolved out of a 1944 ballot initiative, so they are more grounded than in many other places — if not necessarily applied assiduously by county assessors.

The state has a two-tiered system, in which nonprofits first apply to the Board of Equalization, which collects state-mandated fees, sales and sin taxes and certifies exemption eligibility.

But assessors in each of the state’s 58 counties make the final decision on exemptions, after determining whether that property is used in a way that is of “primary benefit” to California.

The meaning of “primary,” however, is widely interpreted. “Although there has to be a primary benefit in California or to Californians, the way we look at primary is not a straight 50 percent test,” said Anita Gore, spokeswoman for the Board of Equalization. “Some activities and things nonprofit organizations do can’t be quantified in that sort of easy way.”

In Los Angeles County, for example, two properties owned by World Vision International, a Christian relief and development organization whose work is largely done overseas, are exempt from property taxes.

Similarly, Direct Relief International, which supplies medical supplies, drugs and equipment to countries around the world, does not pay property taxes on the office building and warehouse it owns in Santa Barbara. “In the current environment, I can imagine why local assessors would be looking for revenue and scrutinizing all the organizations exempted from local property taxes to see if they’ve complied with all the requirements and basically met their end of the policy bargain,” Thomas Tighe, chief executive of Direct Relief, said in an e-mail.

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In San Mateo County, the William and Flora Hewlett Foundation has had a property tax exemption for decades, said Terry Flinn, special assistant to the county assessor.

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So far this year, the Hewlett foundation has granted $14.2 million, or about 27 percent of its total gifts of roughly $52 million, to groups working in California. The rest went out of state and around the globe.

Mr. Flinn said that the foundation holds a long-term lease on the property it occupies, which is owned by Stanford. Both Stanford and the foundation are granted exemption from property taxes by the county each year. “It’s now on our radar as something to look at,” he said.

Lawrence E. Stone, the assessor next door in Santa Clara County, has been one of the staunchest defenders of the primary benefit standard. Santa Clara grants property tax exemption to some 4,000 nonprofit groups, including the Kaiser Foundation Hospitals and Stanford.

Those two nonprofits alone account for about $90 million in tax revenue, were it collected.

Mr. Stone noted that a number of nonprofits that do operate exclusively in California are not eligible for property tax exemption. “I just came from one of the largest Rotary clubs in the country,” Mr. Stone said. “Rotary and other service organizations do a tremendous amount of service in local communities, and they’re not exempt.”

He testified at one of three hearings about the exemption held by the Board of Equalization in 2007 and 2008, after a group of nonprofits led by the International Community Foundation in San Diego complained.

John Walton, the late son of Sam Walton, the founder of Wal-Mart Stores, had given the charity, which works to build support for nonprofits working in Mexico and Latin America, a seven-acre property nine miles from the Mexican border, but the San Diego County assessor had refused an exemption.

That meant the charity was paying about $21,000 in property taxes a year, said Richard Kiy, its president. “A number of the issues we grapple with have cross-border impacts and so have an impact on Californians both directly and indirectly,” Mr. Kiy said.

For example, International Community works with nonprofits in Mexico that are fighting tuberculosis, which is increasing in California because of migration patterns. “Californians benefit from that work,” Mr. Kiy said.

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The board, however, voted 3-to-2 for no change in the rules.

International Community found a way out of its property tax burden by creating a new nonprofit and giving the Walton property to it. That nonprofit, which operates as Olivewood Gardens, runs educational programs on organic gardening and nutrition in California, among other things.

Olivewood Gardens leases a building on the grounds to International Community, which now pays no property taxes. “Imposing property taxes on nonprofits in a global era is clearly just a money grab,” Mr. Kiy said.

Mr. Lion said his client is appealing the board’s denial of the exemption and that it would most likely consider a legal challenge to the primary benefit rule. “I think it’s clearly a violation of the commerce clause of the Constitution, and it may also be a violation of the equal protection clause, given the uneven application of the standard,” he said.