Mexican President Enrique Pena Nieto is facing new threats to his already historically low approval rating after teachers refused to start the academic year in some states and a local news outlet reported he may have plagiarised portions of his thesis when he was in college. On Monday, teachers in the southern states of Chiapas and Oaxaca refused to resume classes after summer break as part of their fight with the president over a new nationwide system of evaluating educators. The CNTE teachers union began blockading highways and airports earlier this year, leading to clashes with authorities in Oaxaca that left at least eight civilians dead and more than 100 injured in June. The standoff occurred as Pena Nieto was accused Sunday by journalist Carmen Aristegui of plagiarizing portions of his undergraduate law thesis in 1991, which contained complete, copied paragraphs that didn’t cite the authors, such as former President Miguel de la Madrid. Pena Nieto’s office said in a statement that the thesis failed to put the material he cited in quotation marks, instead listing the writers he quoted as references in its bibliography. This was just a “style error,” and Pena Nieto met the requirements of Panamericana University, his office said. Pena Nieto’s office declined to comment further. This has been a difficult month for the Mexican president. A poll by Reforma newspaper showed his popularity plunged to 23 per cent, the lowest for any president in almost 20 years. That survey was taken before the Guardian newspaper reported that a businessman paid a property tax on Pena Nieto’s wife’s apartment in Miami. All combined, Pena Nieto’s approval rating is probably headed further south, according to political analyst Jorge Chabat, challenging his ability to govern. “He could get to levels of Dilma Rousseff,” said Chabat, an expert at the Centre for Economic Research and Teaching in Mexico City, referring to Brazil’s suspended president. In the months before the lower house voted in favour of her impeachment in April, the percentage of those who considered Rousseff’s government good or very good dipped below 10 per cent, a record low. “At this point, I don’t see any way for him to have the capacity to move legislative proposals forward,” Chabat said. Those would include security overhauls intended to reduce violence, he said. While there’s very little chance Pena Nieto would be suspended like Rousseff, Chabat said, his ratings are seen as hurting his Institutional Revolutionary Party’s chance of winning state elections next year and the presidency in 2018. On her independent website, Aristegui reports Pena Nieto copied at least 10 authors in his thesis, which he wrote for his bachelor’s degree in law. In Mexico, a thesis for undergraduate work is required at some universities. Pena Nieto later received a masters in business administration from the Monterrey Institute of Technology. Aristegui has investigated Pena Nieto’s family before. She reported in 2014 that the president’s wife, Angelica Rivera, bought a house from a government contractor. While both were cleared by a government investigation of any conflict of interest, Rivera returned the house without executing her purchase option, and public opinion of the president has plunged ever since amid discontent over his response to corruption. Earlier this month, the Guardian published documents showing businessman Ricardo Pierdant had paid taxes in 2013 on Rivera’s US$2 million luxury home in Miami. Pena Nieto’s spokesman said in a statement at the time that Pierdant had no federal government contracts, nor was he competing for one. The president later acknowledged the payment but said Rivera reimbursed Pierdant, who told broadcaster Univision he hasn’t benefited as a businessman from his relationship with Pena Nieto. Pena Nieto has said that he’s more concerned with advancing Mexico than the public’s opinion of him. Standing in front of children dressed in their school uniforms, Pena Nieto pledged Monday there would be no dialogue with educators until they returned to their classrooms. “Teachers in opposition, return to your classes. Education first, dialogue second,” he said.