Boston University will lay off 120 staff members and eliminate 120 unfilled positions while trimming its $2.5 billion operating budget by 5 percent for the 2026 fiscal year. The measures, announced in a message from President Melissa Gilliam, affect roughly 1 percent of the university’s workforce. University leaders cited “recent and ongoing federal actions” that are reducing research grants and operating support, along with rising inflation, shifting demographics and weaker graduate enrollment. The administration has already frozen merit pay increases and warned that further belt-tightening could be required if federal funding continues to fall. Affected employees will receive severance and transition assistance, the university said. BU’s research enterprise, which drew $579 million in external awards last year, and its large population of international students could face additional pressure from the White House’s efforts to restrict student visas and curb spending on academic science.