Indian regulators’ findings that samples of Nestlé SA Maggi instant noodles contained impermissibly high levels of lead stunned middle-class consumers this month. But long before India yanked the product off store shelves, U.S. food-safety inspectors had deemed hundreds of made-in-India snacks unfit for sale in America.

Data on the website of the U.S. Food and Drug Administration show that it rejected more snack imports from India than from any other country in the first five months of 2015. In fact, more than half of all the snack products that were tested and then blocked from sale in the U.S. this year were from India. Indian products led the world in snack rejects last year as well.

Mexico, a much larger trading partner of the U.S., was second in terms of rejections this year, followed by South Korea. China -- whose exports to the U.S. are worth ten times as much as India’s -- was a distant eighth.

And it’s not just snack foods. The U.S. FDA has rejected all sorts of imports from India, including everything from cosmetics to drugs to ceramics.

Illustration: The Wall Street Journal made with Datawrapper

So why did the Indian snacks fail the U.S. FDA tests?

The reasons vary from problems in packaging and labeling to alleged contamination. The FDA website says Indian products have been found to contain high levels of pesticides, mold and the bacteria salmonella.

In one colorful description this February of a product from the western state of Gujarat, which the FDA identified only as “snack foods not elsewhere mentioned,” it said it blocked the import as it “appears to consist in whole or in part of a filthy, putrid, or decomposed substance or be otherwise unfit for food.”

While India’s national food-safety watchdog doesn’t monitor exports, it has been rushing to test everything from soups to pastas to instant noodles sold domestically in the wake of the Nestlé findings.

Sales of Nestlé’s Maggi noodles were officially blocked across the country last Friday, after the Food Safety and Standards Authority said it found them “unsafe and hazardous for human consumption.” Nestlé on Thursday challenged the ban in court and said its own tests hadn’t detected elevated levels of lead, as authorities alleged.

Heightened concern over the safety of processed food in India has pushed the Indian authorities into a testing frenzy. But its chief says he doesn’t have the manpower or facilities to check the millions of packaged products that fill the kitchen cabinets in the world’s second-most populous nation.

“Food-safety is a very sensitive thing in developed countries,” so countries like the U.S. have better food-safety infrastructure, said Yudhvir Singh Malik, the chief executive of the authority. “A lot of that sense is still to come in developing countries.”

Most Indian snacks rejected by the FDA this year were from the Nagpur-based food company Haldiram’s. Among the rejected Haldiram’s products were some sugar candies and salty Indian snack mixes. The FDA said on its website that it rejected the Haldiram’s products because it found pesticides in them.

A.K. Tyagi, a senior-vice president at Haldiram’s, said its food “is 100% safe and complies with the law of the land.” Discrepancies, he said, arise because food-safety standards differ in India and the U.S. “A pesticide that is permitted in India may not be allowed there. And even if it is, they may not allow it in the same concentration as it is here,” he said.

Indian baked snacks also had troubles getting into the States. Out of 217 imported baked products rejected by the U.S. FDA so far this year, more than half were made in India. One of them was a biscuit pack manufactured by India’s largest biscuit-maker, Britannia Industries Ltd.

On its website, the FDA said the packaging of the product didn’t list all ingredients and failed provide consumers adequate nutrition information. Britannia, in response, said it didn’t authorize the shipment.

"Britannia exports to the U.S. only out of U.S. FDA registered factories in India and meets product/labeling standards,” the company said in an email. “These may be instances of shipments made by independent exporters based out of India."