A worker makes clothes at a garment factory that supplies Shein.
New York CNN  — 

US Congress is stepping up the pressure on Chinese fast-fashion giant Shein.

In a letter to the Securities and Exchange Commission Monday, a bipartisan group of 22 US House of Representatives members asked the SEC to require that Shein certify that any of its products that are made in China do not utilize Uyghur forced labor.

“There are credible allegations of the company’s use of underpaid and forced labor in the Xinjiang Uyghur Autonomous Region,” said the letter, led by Reps. John Rose of Tennessee and Jennifer Wexton of Virginia.

The United States has banned all imports from the Xinjiang region over concerns of the use of forced labor.

Lawmakers “are demanding transparency and seeking independent verification — free from state influence — that the company does not use Uyghur forced labor,” according to the letter.

A Shein spokesperson told CNN that the company has no suppliers in the Xinjiang region and it has zero tolerance for forced labor.

The SEC did not immediately respond to a request for comment.

Shein’s mobile app is currently the fourth-most downloaded in the United States, and the company is reportedly preparing an IPO later this year.

Shein, which was founded by Chinese entrepreneur Chris Xu, initially created a cult following for its fast-fashion apparel and has since branched out into other offerings, such as home goods.

Shein commissions its own goods through manufacturers it teams up with in, what is effectively seen as a supersonic version of fast fashion.

The letter illustrates how Congress is scrutinizing Shein and rival fast-fashion app Temu amid their surging popularity in the United States.

Temu was launched by PDD Holdings last year. PDD was founded in China and also owns Pinduoduo, a hugely popular Chinese e-commerce giant that was found in a recent CNN investigation to have the ability to spy on its users.

Earlier this month, a US congressional commission called out Shein and Temu in a report that suggested the companies and others in China were potentially linked to the use of forced labor, exploitation of trade loopholes, product safety hazards or intellectual property theft.

Both Shein and Temu have gained traction stateside by offering extreme bargains to shoppers, many of whom continue to feel the squeeze from historically high inflation.