Europe's premier particle physics laboratory, CERN, has suspended an Italian theoretical physicist after he allegedly denied that physics suffers from a misogynist bias and criticized affirmative-action policies during a presentation at the lab.

The University of Pisa and the European Research Council (ERC), which funds his research, also say that they are opening investigations.

CERN, which lies outside Geneva, Switzerland, announced its decision on 1 October, saying that the physicist, Alessandro Strumia of the University of Pisa, was barred “from any activity at CERN with immediate effect, pending investigation into last week’s event”. Strumia gave his talk on 28 September.

He disputed the characterization of his presentation as sexist in an e-mail to Nature , calling it defamatory.

In its statement, CERN said that Strumia’s remarks were antithetical to its code of conduct and to its values. “CERN is a culturally diverse organisation bringing together people from dozens of nationalities. It is a place where everyone is welcome, and all have the same opportunities, regardless of ethnicity, beliefs, gender or sexual orientation.”

The statement from the University of Pisa’s rector, Paolo Mancarella, acknowledged accusations that Strumia’s slides violated “fundamental values” of the university’s community. Mancarella said that he has deemed those accusations “founded” and opened an ethics investigation.

The investigation will be handled by the university’s ethical committee.

In a statement released on 1 October, the ERC’s president, Jean-Pierre Bourguignon, referred to claims made by an ERC grantee, whom he does not mention by name. The ERC press office confirmed to Nature that he was referring to Strumia.

“I would like to stress that the ERC strongly supports the principle of equal opportunities between women and men, and is committed to improving gender balance and tackling potential gender bias in all its operations,” wrote Bourguignon. He said that he would be contacting CERN to “seek further details” about the grantee’s talk.

Strumia gave his talk at the lab’s first Workshop on High Energy Theory and Gender, in front of an audience largely made up of women. The reaction on social media was quick and fierce. In particular, he was criticized for naming a woman who was hired for a job instead of him. He allegedly said that he should have been hired because his papers received a larger total number of citations.

Strumia, who does research at CERN as an 'invited scientist', told Nature that commenting on CERN’s decisions may contravene the organization’s rules while the investigation is pending. But he added: “I hope they will want to talk and tell me what it was about my talk that was illegal.”

In response to the social-media criticism, Strumia said: “I trust that the honest majority will understand that it is the truth, and that it was worthwhile to suffer such lynching for not submitting to censorship”.