Congress is threatening to void California's ability to set food safety laws, potentially thwarting efforts by the state attorney general to require warnings for such contaminants as mercury in tuna and acrylamide in potato chips.

Activists warn that the measure is yet another attack on California's Proposition 65, the landmark 1986 law requiring warning labels on items known to contain carcinogens or reproductive toxins.

But supporters — including 12 California representatives — say the measure is necessary to establish uniform food standards in what is increasingly a global economy. California's concerns over trace amounts of potential carcinogens, they add, improperly taints the safest food supply in the world.

"We too often spend way too much time chasing 'parts per billion' and 'parts per trillion' without a careful examination as to where do you get the best bang for your buck in protecting health and safety for consumers," said Rep. Jim Costa,

D-Fresno. "Unfortunately, aspects of Proposition 65 fail in that case." HR 4167, the "National Uniformity for Food Act of 2005," would give federal regulators sole power to determine what foods on the grocery shelf would require such warnings.

Activists fear the only uniformity the bill would achieve is the uniform absence of food safety laws. The federal government remains largely silent on food safety standards and warnings, with the Food and Drug Administration devoting most of its attention to pharmaceuticals, said Joe Guth, executive director of the California League for Environmental Enforcement Now.

The bill allows states to petition to make their local requirements — such as a Proposition 65 warning — the national standard. But Guth sees that as an empty promise.

"The FDA's whole posture is they don't like these regulations," he said. "It makes it very unlikely they'd approve a whole bunch of state laws, at least in any timely way."

If the bill becomes law, 80 different food safety laws in 37 states would be repealed, according to Rep. Henry Waxman, D-Los Angeles, who voted against the measure in committee last month.

Congress, he said then, "doesn't have a scrap of evidence in the record as to why that might be a good idea."

"It's a radical change in the law," he added.

State regulations would stay in effect while the agency reviews the petition.

Defenders of Proposition 65 have seen attempts to repeal the measure almost every year since voters approved it in 1986. Alarming them this year are the 226 lawmakers who have signed on as co-sponsors to HR 4167 — eight more than necessary to pass the bill in the House.

The 12 co-sponsors from California, including Costa, Guth said, are poised to provide the margin of victory the measure needs.

Added David Roe, principal author of Proposition 65, who is now a partner in the San Francisco law firm Calvo & Clark, LLC: "The bill is a clone of things we've seen before. The language it uses is uniformity, as in 'Wouldn't it be awful to have 50 different labels?' The reality is ... there aren't even two labels. But there is a pressure to clean up toxic chemicals."

Proposition 65's power, Roe said, is the "quiet compliance" it exacts from industry. When pressured, manufactures usually clean up their products rather than add a warning label.

The food industry doesn't see HR 4167 as the death of Proposition 65, despite its longstanding opposition to it. Instead, said Stephanie Childs, spokeswoman for the Grocery Manufacturers Association, the resolution offers a way to make California's warnings and concerns available to the entire nation.

"There's no reason, if a state feels there is a cause for concern, ... that all residents of all 50 states shouldn't have that information," Childs said. "What national uniformity would do is give California the opportunity to bring its science to the national level."