With just four weeks left in the semester, non-tenure track faculty at Wellesley College walked off the job Thursday morning, citing an impasse after 10 months of failed contract negotiations with administrators.

The union, Wellesley Organized Academic Workers, said compensation, workload, and other benefits remained key sticking points.

The walkout left some students with classes taught by striking teachers scrambling, leading to concerns that they may not receive full credit for incomplete coursework.

Leah Okumura, a senior instructor in the biological sciences department and a striking union member said salaries were frozen after the 2008 financial crisis and have not kept pace with the high cost of living in Greater Boston. She said starting salaries were commonly as low as $55,000 as recently as five years ago.

“Over the past few years we’ve gotten a couple of increases, but salaries are really not enough to live on,” she said. “In addition, there are a number of benefits that tenure track faculty get from the college that non-tenure track faculty don’t receive.”

Those include a mortgage benefit to help buy a house in the area, and a tuition benefit to help send the children of faculty to college,“ she said.

Workload was another point of contention in negotiations, with the college proposing that many unionized faculty teach five courses a year, up from four. Okumura called that a 25% increase in workload that would drastically change the nature of their jobs. Unlike adjunct faculty who only teach on short-term contracts at many other schools, Okumura said non-tenured faculty at Wellesley are longer-term staff that take on many of the same responsibilities as tenured professors.

“We help students with research. We advise them in their major, first-year advising, premed advising, all kinds of things like that,” she said. “In addition, we just spend a lot of time getting to know our students. And it’s one of the things that makes Wellesley College a really great place to be as a student.”

Wellesley President Paula Johnson issued a statement expressing disappointment in the decision to strike but pledged to continue negotiating in good faith.

The college set up a web page with the details of its latest proposal to the union, including what it said would be an almost 30% increase in overall compensation over 4 years.

About a third of faculty at the prestigious women’s college are non-tenure track. The school says it doesn’t have exact numbers on how many students have been impacted by the strike, but that it would only grant half credit for classes left incomplete due to the walkout.

In a campus-wide email , Provost Courtney Coile said federal regulations dictate the number of “contact hours required to earn college credit and the number of credits a student must be enrolled in to maintain full-time status for financial aid and visa eligibility purposes.”

Coile acknowledged that could negatively impact some students but said the college is helping students maintain full credit by allowing them to transfer into ongoing classes taught by tenure track faculty if they choose.

The union has criticized docking students’ credit, accusing the college of using their own students ability to graduate as a bargaining chip.

“This is ludicrous,” Okumura said. “It’s totally unprecedented to take away credit from students in retaliation for a faculty strike.”

In an opinion piece in the campus newspaper, The Wellesley News, student Riannon Last blasted the college’s proposal for making up any lost credits as unrealistic.

“[T]he college has willingly decided to threaten students with losing their financial aid or visa status if they do not attend scab lectures or replace their current lectures with completely unrelated courses that are halfway through their content. This disgusting move by the college is deliberately meant to harm students.”

School spokesperson Stacey Schmeidel disputed that characterization, saying the college has provided options for students.

Negotiations will resume next week.