The U.S. federal authorities are reportedly investigating stablecoin issuer Tether for possible illicit use.The Wall Street Journal (WSJ) released an exclusive report suggesting criminal probes by the U.S. Attorney's Office and the freezing of Tether.Tether CEO Paolo Ardoino denies the allegations, stating that there is no sign of Tether being under investigation.The news caused a drop in the prices of Bitcoin, Ethereum, and other cryptocurrencies.