Nicki Minaj is suing blogger Nosey Heaux for $75,000 (S$105,447) for calling her a "cokehead."
The rapper, 39, claims Nosey – real name Marley Green – shared a video Monday (Sept 12) that included allegations the singer used drugs.
Page Six said it had seen court documents showing Nicki was taking action.
The outlet said Nosey allegedly said on social media: "(Minaj is) shoving all this cocaine, shoving in all this cocaine up her nose. Allegedly. Thank you. Allegedly. But we all know it's true.
"F***, listen, I can't even say allegedly with that 'cause I…we all know it's true. I'm not saying allegedly on that. Nicki Minaj is a cokehead."
Nicki is also said to be angry with Nosey Heaux for apparently making disparaging comments about her 12-month-old son, who she shares with husband Kenneth Petty.
Petty, 44, is a registered sex offender convicted of attempting to rape a 16-year-old girl in 1994 and Nosey is said to have claimed the couple's son will need therapy to stop him being a "rapist".
Nicki's attorney, Judd Burstein, told Page Six: "Marley Green is a disgrace – someone so lacking in fundamental decency that she has posted vile comments about Nicki's one-year-old son.
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"When this case is over, she will no longer be permitted to use the name 'Nosey Heaux' because we will take her trademark from her when she does not have enough money to pay the judgment.
"Anyone else who spreads lies about Nicki will suffer a similar fate. My marching orders are to aggressively sue anyone with a media or social media following who damages her with intentional lies.
"Eventually, the lesson will be learned."
Page Six adds Nicki wants damages of $75,000 from Nosey for defamation.
Nosey shared screengrabs of an apparent Instagram direct message exchange with Nicki in response to the legal filing.
It shows Nicki allegedly saying: "We know you don't really have any money to speak of so losing all this little advertisement money from YouTube will make a huge dent. You'll only be the first of many tho."
Nosey hit back: "Are you ok Nicki? File your lawsuit ok? I'm not afraid and I won't be intimidated," prompting Nicki to respond: "Yaaaayyyy!!!!"