Duke University workers won’t get a jury trial in their lawsuit challenging how the private college managed its retirement plan.

The workers also won’t be able to file a third amended lawsuit to add new claims because they failed to show good cause, Judge Catherine C. Eagles of the U.S. District Court for the Middle District of North Carolina held June 11 in a two-page order.

The ruling comes one month after the employees urged the court to allow them to present their case in front of a jury instead of a judge. The employees’ jury request followed Duke’s announcement...