Tether, the crypto company best known for issuing the world's largest stablecoin, said Thursday it has frozen $344 million worth of USDT tokens across two wallets on the Tron blockchain after receiving requests from U.S. authorities.

The freeze was carried out after authorities flagged the addresses for alleged links to illicit activity, the company said in a blog post on Thursday. The action prevented further movement of the funds.

The company did not specify the nature of the activity or who controlled the wallets. Blockchain analytics firm AMLbot said the addresses appeared in scam-related documents and posts.

The move comes as debate around the role and responsibility of stablecoin issuers in stopping funds linked to illegal money transfers is back in the spotlight. The Financial Action Task Force recently warned that stablecoins are increasingly used for illicit transactions, including sanctions evasion and money laundering. Public blockchains allow transactions to be traced, while issuers retain the ability to freeze assets under certain conditions.

The issue came into focus this month following the $285 million exploit of Drift Protocol, in which attackers moved hundreds of millions of USDC stablecoin and bridged funds across chains. Critics argued that Circle (CRCL), the issuer of USDC, could have acted faster to freeze assets and limit losses, while the company said it only takes such actions when legally required or at request by law enforcement and authorities.

Tether said it works with law enforcement when wallets are tied to sanctions evasion or criminal networks, and has supported more than 2,300 cases globally across 340 agencies in 65 countries.