The National Science Foundation has placed a hold on new grants for Duke, Harvard, Princeton, and Yale, according to internal agency documents reviewed by Nature. The reporting said NSF limited future awards for these universities while allowing previously awarded funding to continue. The documents described delays in proposal processing at the Office of Award Management, including paused submissions and longer review windows compared with standard timelines. NSF declined to comment when asked for explanation. For research-intensive universities, the action signals heightened volatility in federal grant operations and adds scheduling risk for labs planning near-term projects, hiring, and equipment purchases. Separately, NSF lifted a hold on some grants for Harvard and other universities after media inquiries, indicating that communications and oversight escalation may be shaping enforcement in real time.