(CNN) A Drexel University professor who received death threats after posting several controversial tweets said Thursday he is resigning because the year-long harassment has made his situation "unsustainable." George Ciccariello-Maher, a professor of politics and global studies, had been teaching his class remotely via video conference after being put on administrative leave, a move that Drexel said was for his own safety. The professor said his resignation is effective December 31. "This is not a decision I take lightly; however, after nearly a year of harassment by right-wing, white supremacist media outlets and Internet mobs, after death threats and threats of violence directed against me and my family, my situation has become unsustainable," Ciccariello-Maher wrote on his Facebook account. "Staying at Drexel in the eye of this storm has become detrimental to my own writing, speaking, and organizing."George Ciccariello-Maher says the threats began a year agoHis situation has raised questions about free speech on campuses
Ciccariello-_ drew more outrage in March after tweeting that he was "trying not to vomit" watching someone give up their first-class seat for a uniformed soldier. Drexel said in a statement Thursday that Ciccariello-_ was leaving to "pursue other opportunities" and that it wished him well.