Shein's IPO could raise billions. Here's what to know about the secretive Chinese-founded company.

Shein, the fast-fashion giant that's built a following through social media influencers touting a seemingly endless variety of new designs, has filed confidentially for an IPO in the U.S., according to the New York Times and Reuters.

Confidential filings are permitted by the U.S. Securities and Exchange Commission, but if the IPO moves forward, the filing — which would include details about the company's financial operations, executives and more — would eventually become a public document.

That would allow everyone from potential investors to customers to take a peek inside a company that's kept much of its operations under wraps. Despite its tight lips, Shein has sparked plenty of controversy inside the U.S., ranging from lawsuits over alleged copyright violations to questions from lawmakers about whether the fast-fashion company relies on forced labor in China.