The U.S. Commodity Futures Trading Commission sent subpoenas on Dec. 6 to virtual-currency venue Bitfinex and Tether, a company that issues a widely traded coin and claims it’s pegged to the dollar, according to a person familiar with the matter, who asked not to be identified discussing private information

Tether’s coins have become a popular substitute for dollars on cryptocurrency exchanges worldwide, with about $2.3 billion of the tokens outstanding as of Tuesday. While Tether has said all of its coins are backed by U.S. dollars held in reserve, the company has yet to provide conclusive evidence of its holdings to the public or have its accounts audited. Skeptics have questioned whether the money is really there.

A document on Tether’s website, compiled by accounting firm Friedman LLP, shows it had $443 million and 1,590 euros ($1,970) in bank accounts as of Sept. 15. Tether tokens were valued at $420 million that day, according to Coinmarketcap.com. Tether hasn’t identified the banks where that money was held, and their names were blacked out in the document.Friedman said in its report that it didn’t investigate the reliability of Tether’s records. The accounting firm and Tether have recently cut ties, Tether said in a separate statement Monday.

Bitcoin, the biggest cryptocurrency by market value, tumbled 10 percent on Tuesday. It fell another 3.2 percent to $9,766.41 as of 9:19 a.m. in Hong Kong, according to composite pricing on Bloomberg.

Actually, this news make bad affect on cryptocurrency market, in CMC all top coins get negative growth.
If Tether really cannot provide conclusive evidence of its holdings, USDT will drop down strongly which cryptocurrency market's in bloodbath one more time.