French farmer Jose Bove, a prominent protester against globalisation and junk food, said today he was denied entry to the United States and speculated large corporations were behind the move.
Mr Bove said he arrived at New York's John F Kennedy International Airport with a valid US entry visa yesterday afternoon but was detained for several hours and later returned to Paris.
"They took my passport from me and said 'You're not allowed to come in for all the things you've done over the years, for speaking out,'" Bove said.
He had been scheduled to speak today and tomorrow in New York at an international conference of academics and trade unionists. Organizers of the conference, on globalisation and labour, included Cornell University's Global Labor Institute.
US immigration officials did not return calls seeking comment, but the French foreign ministry said he had been refused for a mistaken response to a question about his criminal record.
Mr Bove said he was surprised at being turned back because he has visited the United States several times, most recently in 2005.
The Frenchman rose to fame in the late 1990s for denouncing agricultural free trade and genetically-modified food, and spent six weeks in jail in early 2003 for smashing up a McDonald's restaurant. He was sentenced to four months in prison in November for destroying a field of genetically modified corn in southern France.
A conference spokesman said calls to the US Immigration Department and to the Department of Homeland Security by the group and US Senator Hillary Clinton's office failed to secure an explanation for Bove's expulsion.
Dr Sean Sweeney, director of Cornell's labor institute, told the conference's opening session, "This speaks volumes about where the United States is in terms of free speech."
A French foreign ministry spokesman said Mr Bove made a "mistake in understanding" when he responded to a question on an immigration form by saying he did not have a criminal record. Bove thought the question referred only to the US justice system, the spokesman said.
In December, Hong Kong denied Bove entry to attend a World Trade Organization meeting.