A $9,000 designer sweater made out of the ultrarare fur of a South American animal called a vicuña is not exactly a typical area of focus for a member of the U.S. Congress.

But when Representative Robert Garcia, a first-term California Democrat and the first Peruvian-born person to serve in the House, saw reports that the luxury design house Loro Piana was not fairly compensating Indigenous workers in Peru who source the rare wool in some of its priciest knit clothing, he decided to use his position to make some noise.

“As the first Peruvian American member of Congress and co-chair of the Congressional Peru Caucus, I write regarding concerning reports about the sourcing of vicuña wool by Loro Piana, a subsidiary of LVMH Moët Hennessy Louis Vuitton,” he wrote to company executives last month.

He demanded that the fashion house — whose products including shirts, scarves and coats can cost anywhere from $500 to $30,000 — explain how it could raise its prices so steeply while steadily reducing the amount it was paying the people who harvest the raw materials for it.

“While Loro Piana’s prices have increased, the price per kilo for fibers paid to the Lucanas community has fallen by one-third in just over a decade; and the villages’ revenue from the vicuña has fallen 80 percent,” Mr. Garcia wrote.

The clash between the 100-year-old Italian clothing brand, whose nondescript knits serve as elite talismans only recognized by the most devoted consumers of fashion, and the freshman lawmaker is just one example of a staple of Congress: lawmakers — many of them with unique backgrounds and personal stories — using their platforms and oversight powers to weigh in on issues that matter to them.

“When we’re talking about a collection of brands that the world knows like Louis Vuitton and others that people aspire to or want to have, I think people should know that the things they’re buying are being made with exploitation,” Mr. Garcia said in an interview.

“These folks are getting, in my opinion, completely exploited for $9-, $10- and $12,000-dollar sweaters — it’s horrible,” he added.

Mr. Garcia said he does not consider himself much of a fashion icon. The suits he wears to work are from Men’s Warehouse. And despite being the older brother of a celebrity stylist — his sister Dianne has dressed the likes of Rosalia and SZA in countless designer get-ups — he says the most luxurious options in his own closet are years-old sweaters bought at a steep discount from his days working at Banana Republic.

But he decided to weigh in with Loro Piana after a Bloomberg report last month that delved into the relationship between the multibillion dollar company, a subsidiary of the LVMH Moët Hennessy Louis Vuitton luxury goods empire, and members of the Peruvian Indigenous community who harvest and sell the fur from the Andean vicuña, the small golden-brown furred cousin of the alpaca.

Vicuña wool is regarded as the “fiber of the gods” and was once considered a sacred fabric worn by Incan royalty. The animal was revered in Indigenous folklore as a reincarnated maiden wrapped in a gold coat. Today, the fine, lustrous fur is the source of one of the most expensive fabrics available.

Loro Piana wields its influence through rare materials with out-of-reach prices, as one of the most prized brands within the conglomerate operated by the wealthiest man in the world.

Matthieu Garnier, the chief executive of Loro Piana North America, disputed the Bloomberg report and pushed back against Mr. Garcia’s inquiry.

The Bloomberg article “did not fairly or accurately characterize the reality of the way vicuña fiber is harvested in Peru, as well as Loro Piana’s genuine and longstanding engagement with the community,” Mr. Garnier wrote in a response to Mr. Garcia’s letter reviewed by The New York Times.

He went on to highlight the company’s conservation efforts in the region and argued that it had played an essential role in helping the vicuña population in Peru climb back from near extinction because of overhunting. The company did so, Mr. Garnier wrote, “by offering a purchase price for sheared vicuña fiber high enough to provide real economic opportunities.”

He said Loro Piana pays workers “in accordance with local practices” — typically once per year when the wool from the animals is collected — and compensates “the independent organizations responsible for the harvest.” He did not address specific claims that the company has paid less in recent years but asserted that Indigenous people themselves have rejected some of the claims of exploitation.

Mr. Garcia said he was unsatisfied with the response and would continue to press for changes.

“Just saying that you’ve invested in some education and in some infrastructure improvements is — that’s not enough,” the congressman said. “This is happening all across South America, Peru and across the world in these kind of lower-income communities, and it’s especially true in communities that are native or Indigenous to those countries. That’s where the most exploitation happens because these folks have so little access to resources.”

In recent years, lawmakers have found rare bipartisan consensus in taking on the biggest players in businesses around the world and across industries, including questioning labor practices at Amazon, the world’s largest online retailer, and a push to force TikTok’s Chinese parent company to sell the popular social media app.