Blackfishing is a word used to accuse someone of pretending to be black or mixed-race.
Nicki, who features on the song, said on Instagram: "Y'all gotta stop."
She added on Twitter: "If you know someone has been suicidal from bullying in the past, why try to get a bunch of people to bully them again about something else?"
The pair went on Instagram live to promote the single.
Jesy said she was "in a group with two women of colour for nine years" and the subject was never brought up until they recorded her last video with the group, Sweet Melody.
