The union said the decision affects hundreds of instructors, most of them undergraduates in the Electrical Engineering and Computer Sciences (EECS) department. But the university said the decision applies only to that department. The university must make retroactive payments to those instructors who didn't receive the benefits since July 2017, Iyengar said.
"The university and the EECS faculty believed that appointments should be kept at 20% or less in order not to interfere with student academic performance," campus spokeswoman Janet Gilmore said in a statement.
A student instructor hired at 20% full-time employment last fall could receive about $7,500 from UC Berkeley under the decision, the union said.
The arbitrator has also directed EECS to stop hiring graduate and undergraduate student instructors below 25% full-time employment, Gilmore and Iyengar said.
The arbitrator's decision came amid a surge in the hiring of student instructors at below 25% full-time employment since 2015, the union said, citing its analysis of university data.