Stablecoin issuer Tether has frozen roughly $225 million worth of USDT ( USDT ) as part of a United States Department of Justice investigation into a Southeast Asian human trafficking syndicate.

In a Nov. 20 announcement, Tether said it had worked with the DOJ and crypto exchange OKX to freeze $225 million worth of USDT in “external self-custodied wallets.” The firm reported the illicit funds had been used by a crime syndicate responsible for a “pig butchering” romance scam — a technique where bad actors attempt to develop an online relationship with unsuspecting individuals, often convincing them to invest in legitimate businesses before conning them.

According to Tether, the USDT freezing followed a “months-long investigative effort” into the location of the funds between the firm, OKX, the DOJ and U.S. law enforcement agencies. The stablecoin issuer said it would work with U.S. authorities to unfreeze any “lawful” wallets that may have been seized as part of the effort.

“Through proactive engagement with global law enforcement agencies and our commitment to transparency, Tether aims to set a new standard for safety within the crypto space,” said Tether CEO Paolo Ardoino. “Our recent collaboration with the Department of Justice underscores our dedication to fostering a secure environment. We believe in leveraging technology and relationships, such as our collaboration with OKX, to proactively address illicit activities and uphold the highest standards of integrity in the industry.”

Impressive work by @Tether_to and @okx teams, alongside with Law Enforcement to stop bad guys https://t.co/P0U8ydP91x

— Paolo Ardoino (@paoloardoino) November 20, 2023

Tether has previously worked with global law enforcement agencies to freeze assets allegedly linked to criminal syndicates, such as when the firm coordinated with Israel’s National Bureau for Counter Terror Financing to freeze roughly $873,000 worth of USDT  reportedly used for funding terrorist activities in Israel and Ukraine. The latest $225-million freeze appears to be the largest in Tether’s history.

Related: Circle, Tether freezes over $65M in assets transferred from Multichain

Unlike many cryptocurrencies, such as Bitcoin ( BTC ), which can be held outside the control of anyone but the individual with the private keys, stablecoins like USDT are more likely to be issued by a single authority. As a result, the issuers sometimes can freeze funds and halt  transactions in response to requests from law enforcement.

However, crypto moving through exchanges is sometimes subject to the same treatment. In August 2022, Binance said it had restricted account access to $1 million in crypto for a Tezos tool contributor following a request from authorities and similarly froze accounts linked to Hamas militants in October 2023 in response to Israeli law enforcement.

Magazine: US enforcement agencies are turning up the heat on crypto-related crime