Union members are demanding furloughed University of Massachusetts workers be called back as the college system faces a $433 million budget shortfall — and possibly another round of cuts. “To be honest, those affected feel like they’ve been stabbed in the back. They are not wanted, nor important, to the mission of this university,” UMass Amherst Staff Association President Leslie Marsland told President Marty Meehan and trustees during Thursday’s meeting. Marsland and other union leaders criticized how the UMass system has handled furloughs and layoffs since the pandemic shut down in-person learning last spring, putting more than 1,000 staff on longterm furloughs statewide.