SAN FRANCISCO (AP) — A federal judge is threatening to force Pacific Gas & Electric to hire more tree trimmers to reduce the chances of its electrical grid igniting fires in Northern California. The judge notified PG&E on Thursday that he expects more precautions to be taken. It comes a day after the San Francisco company acknowledged that as many as 22,000 trees may still be creating fire hazards. The judge is overseeing requirements imposed on the nation's largest utility after its natural gas lines blew up a neighborhood a decade ago. PG&E has asserted it can safely maintain the millions of trees in its territory.