One Nation leader Pauline Hanson is being investigated over a "racist" tweet where she told a Greens senator to "go back to her country".
Senator Mehreen Faruqi sent Senator Hanson's tweet on to the Australian Human Rights Commission with her confirming on Friday an investigation had been launched.
"I'm glad the Human Rights Commission has accepted my complaint. Racism must be held to account," she said.
Senator Hanson is being investigated over the tweet she wrote in reply to a post Ms Faruqi shared criticising the monarchy in the wake of Queen Elizabeth II's death.
"I cannot mourn the leader of a racist empire built on stolen lives, land and wealth of colonised peoples," the tweet said.
Ms Hanson told the senator to go back to her native country of Pakistan.
"Your attitude appals and disgusts me. When you immigrated to Australia you took every advantage of this country," she wrote.
"You took citizenship, bought multiple homes, and a job in a parliament. It's clear you're not happy, so pack your bags and piss off back to Pakistan."
Greens leader Adam Bandt has welcomed the investigation, telling the ABC on Friday the tweet was "despicable".
"Members of parliament ... should have the ability to contribute in the public debate without attacks of racism, and to be told to go back to where they come from.
"When people use the bull pit of parliament to make racist attacks on people, it should be condemned."
Greens attempt to censure Pauline Hanson
The Greens attempted to censure Senator Hanson in the chamber last month but the motion was amended by the government and opposition to instead condemn all forms of racism.
Senator Hanson has defended her tweet and denied she is racist. She said her comments were a critique of Senator Faruqi's post.
"Criticism is not racism," Senator Hanson told the Senate on September 27.
"(The Greens) see themselves as the epitome of virtue who can say or do nothing wrong. Their sense of entitlement and privilege is stunning."
Senator Faruqi claimed Senator Hanson had crossed the line between robust public debate and racism.
"I and everyone like me ... have every right to participate in public debate," the NSW representative said.
"I will not be silenced, especially on the topic of the British monarch and monarchy.
"The truth about the empire must be told. I have the right to talk about this history without being racially vilified."
Following the tweet, Senator Hanson doubled down on her comments made online, saying she would not retract her comments.
She also offered to take Senator Faruqi to the airport, which led Greens senator Jordon Steele-John to call her a "scumbag" in the chamber.
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