Last Wednesday marked an important day for adjunct instructors across the United States. It was the first “National Adjunct Day of Action,” which sparked demonstrations and walk-outs at universities across the U.S. to draw attention to the working conditions of part-time professors.

One major demonstration took place at University of North Carolina, where adjuncts comprise 59% of the faculty. Adjuncts say that the system is exploiting them — and that the adjunct system affects students negatively as well.

Since the early 1980s, universities and colleges in the United States have been using adjuncts to teach core undergraduate curriculum in increasing numbers. Adjuncts are hired at the associate professor level without tenure; in more and more cases, work full-time.

Adjuncts say that universities take advantage of their skills and while offering little pay and often no job security at all. These professors are usually hired by the semester and paid per course.

As adjunct professor at SUNY Plattsburgh Karen Hildebrand writes, in an essay published on the Washington Post, the purpose of the National Adjunct Day of Action was to “achieve parity” with full-time tenured professors — to be paid better, to have more job security, and to have equal professional development opportunities.

Hildebrand has been an adjunct instructor for 20 years.

According to Chapel Hill News, more than 82% of UNC’s adjuncts work full-time. One of the major here is the disparity in pay. The average salary for a full-time adjunct instructor at UNC between 2013 and 2014 was $53,172. The same for a tenured professor is about twice that at $110,000.

“While no one likes pay disparity of any type, being a lower-paid adjunct often comes with much more flexibility in scheduling and/or no research or publishing responsibilities,” says Rick Friedman, President, ScholarlyHires.com. “It’s a trade-off of sorts.”

Many of the adjuncts who teach at the roughly 1,800 colleges and universities throughout the U.S. felt that they would risk their jobs by participating in walk-outs, but students and tenured professors both showed their support by taking active roles in the demonstrations.