Many of the message recipients are university students, with the first texts sent the morning after the US presidential election.
Dozens of black Americans have received text messages telling them they had been “selected” to pick cotton “at the nearest plantation”.
The messages invoking slavery were sent to university students from colleges including Ohio State University, Clemson University in South Carolina, the University of Southern California and Missouri State University, according to Sky’s US partner network NBC News.
But other black men, women and children were recipients of the messages in several other states including New York, Alabama, Pennsylvania, Maryland and Tennessee.
The first messages were sent the morning after the US election, with some referencing president-elect Donald Trump.
The FBI said in a statement on Thursday that it is aware of the texts and has been in contact with the US Department of Justice. It also encouraged people who receive the messages to report them to local law enforcement.
The Federal Communications Commission also said it is investigating alongside federal and state law enforcement.
The attorney general’s office in Virginia condemned the messages on Wednesday and directed anyone who “believes themselves to be under threat” to contact law enforcement. Police departments and leaders in cities across the country have also addressed the situation.
It is unclear who is behind the mass messages, what motivated them, or how they obtained the phone numbers.
