Australian author Yassmin Abdel-Magied has been kicked out of the United States at the border after immigration officials said she didn't have the right visa.
The 27-year-old Muslim activist, who recently moved to London, flew into Minneapolis on Wednesday night, local time, but just three hours later was ordered onto another plane out of the US.
Ms Abdel-Magied had tweeted that she was on her way to speak at an event called "The M Word: No Country For Young Muslim Women".
United States Customs and Border Protection said all visitors must have the right travel documents.
"CBP officers determined this individual did not possess the appropriate visa to receive monetary compensation for the speaking engagements she had planned during her visit to the United States," a spokesman said in a statement on Thursday.
"As such, she was deemed inadmissible to enter the United States for her visit, but was allowed to withdraw her application for admission.
"The traveller is eligible to reapply for a visa for future visits."
Ms Abdel-Magied said immigration officials at Minneapolis airport had "taken my phone, cancelled my visa and are deporting me".
"Well, guess that tightening of immigration laws business is working, despite my Australian passport. We're taking off now. What a time..."
Ms Abdel-Magied said the airport officials also took her passport.
"Apparently I can't be trusted with it until I'm in a foreign country because, as Officer Blees said, 'planes get turned away back way too often and then...," she tweeted.
She moved to London in 2017 after suffering a backlash due to a Facebook post on Anzac Day that said: "Lest We Forget (Manus, Nauru, Syria, Palestine ...)".
The post was deleted a few hours later, with Ms Abdel-Magied apologising and acknowledging "that the timing and nature of the post was disrespectful".
The US Supreme Court last December gave the green light to President Donald Trump's controversial travel ban that targets people from six Muslim-majority countries.
The ban was subject to several legal challenges after opponents said it was in violation of the US Constitution because it discriminates against Muslims.
Australia's Citizenship and Multicultural Affairs Minister Alan Tudge said he did not know the details of the case, but it was "unusual for an Australian citizen to not be granted a visa to go into the United States".