FILE - In this June 2, 2016, file photo, a woman holds hats to get them autographed by Republican presidential candidate Donald Trump during a rally in San Jose, Calif. Trump’s “Make America Great Again” hats proudly tout they are “Made in USA.” Not necessarily always the case, an Associated Press review found. (AP Photo/Jae C. Hong)
FILE - In this June 2, 2016, file photo, a woman holds hats to get them autographed by Republican presidential candidate Donald Trump during a rally in San Jose, Calif. Trump’s “Make America Great Again” hats proudly tout they are “Made in USA.” Not necessarily always the case, an Associated Press review found. (AP Photo/Jae C. Hong) Credit: Jae C. Hong

Washington — Donald Trump says he won’t stand for it if it turns out some of his hats labeled “Made in USA” actually weren’t made entirely in the USA.

The baseball-style “Make America Great Again” hats are indeed stitched together at a small factory in the Los Angeles area. But in a small sample tested by The Associated Press and an outside expert, at least one did not contain the specific type of U.S.-made fabric the manufacturer insists is always used for the hats.

The true origin of the fabric in that hat remains a mystery — whether U.S. or foreign made. It shows how difficult and murky it can be to verify something is actually “Made in USA.”

Informed of AP’s findings, Trump said any misrepresentation would be unacceptable. He said: “I pay a good price for that hat. If it’s not made in the USA, we’ll bring a lawsuit.”

The AP review included a microscopic analysis of five hats bought from Trump’s campaign website. The analysis showed the fabric in one was of a different type than that made by the supplier the manufacturer told the AP provides all his hat fabric.

In addition to the fabric analysis, two of the manufacturer’s employees, including a top sales agent, said the hats’ fabric, bills and stiffeners were imported.

The factory’s owner, Brian Kennedy of Cali-Fame of Los Angeles Inc., said the two employees were wrong, but he refused to explain the fabric discrepancy. Federal law requires that items labeled “Made in USA” be made from materials “all or virtually all” from the United States.

“I’m not using imported materials,” Kennedy said. “We’re playing by the rules.”

On a broad level, the tale of Trump’s hats shows the challenge of revitalizing U.S. manufacturing, which has been ravaged by cheap competition from overseas. Trump has accused Asian countries of unfairly manipulating their currencies to boost exports.

Labor costs in Asia are so low that hats or other clothing can cost less than half the price of products made in the United States. Asian fabric prices are also lower, though less dramatically. While Trump has tried to get Made in USA hats for his campaign, knockoffs of those hats, clearly made in China, do a brisk business for other vendors. And Trump’s private companies and the clothing line run by his daughter, Ivanka, routinely sell clothes and other products made in China and other Asian countries.

Trump has warned Ford Motor Co. that he would place a 35 percent tax on cars sent to the U.S. from a planned plant in Mexico, and he has pledged to “get Apple to start building their damn computers and things in this country.”

But the Trump campaign’s experience shows how difficult it can be to be utterly certain of a product’s provenance. Trump told the AP that his staff had visited Cali-Fame’s factory and reviewed paperwork guaranteeing the hats qualified for Made in the USA labeling.

“It was very important to us that these hats be made in the USA,” he said.