The 76 cases of alleged plagiarism account for at least 17.2% of Hahn's doctoral thesis, according to an expert opinion commissioned by the opposition Green Party in Hahn's native Austria.
The commissioner wrote his PhD thesis in 1987 at the University of Vienna at a time when programmes that scan for plagiarism were not commonplace. It is entitled 'Perspectives of Philosophy Today – with the example of the city phenomenon'.
This is not the first time Hahn has been accused of plagiarism over his thesis. He was first under the spotlight in 2007, when he was science and research minister with Austria's conservative ÖVP party.
At the time, an expert commission found no sign of plagiarism in his work.
But in the wake of recent plagiarism scandals in Germany, it seems that Hahn's detractors are determined not to let him off the hook.
Former German Defence Minister Karl-Theodor zu Guttenberg, a rising political star who was seen as Chancellor Angela Merkel's political heir, was forced to resign at the beginning of 2011 over a plagiarism scandal. A coalition of citizens and academics had accused him of lifting large sections of his doctoral thesis from outside sources without referencing the information.
More recently, a vice-president of the European Parliament, Silvana Koch-Mehrin MEP (Germany; Alliance of Liberals and Democrats for Europe) stood accused of copying 25% of her doctoral thesis.
She announced her resignation from her functions as Parliament vice-president and leader of the German liberal delegation in May, saying she wanted the investigation by the University of Heidelberg to be conducted peacefully. Koch-Mehrin remains as a regular MEP.
Political consequences for European Commission?
In the case of Hahn, the expert opinion was commissioned by Peter Pilz, an Austrian MP from the opposition Greens party. The analysis of the academic work was conducted by Austrian media researcher Dr. Stefan Weber, who had already filed plagiarism accusations against Hahn in 2007.
Commissioner Hahn's press office refuted the allegations. In a statement, his aides stressed that the thesis had already been scoured to no avail. And the conclusions of another analysis of the doctoral work, conducted by the University of Vienna, where Commissioner Hahn did his doctorate, are yet to be disclosed, the press office said.
As for the expert opinion by Stefan Weber, Hahn's cabinet said it was "politically motivated". Consequently, the results could not be trusted, his office said.
For now, Johannes Hahn's position as commissioner for regional policy is safe. Should the allegations be confirmed, it seems very unlikely that the Commission would force him to leave given the relatively minor nature of the allegations.
For the European Parliament, the only option would be to hold a vote of no confidence against the entire Barroso Commission, which seems unlikely. The fall of the Santer Commission in 1999 was motivated by much more severe allegations of corruption and embezzlement against Commissioner Edith Cresson.
If the matter gets more serious, Hahn could of course also choose to resign on his own initiative.
Based on reporting by EurActiv.de