The specter of nursing strikes is looming on both coasts, as newly empowered nurses’ unions confront hospitals pressed to cut costs amid changes in health care financing.

In New York, over 6,000 registered nurses are poised to walk out of three of the city’s most prestigious hospitals before the year’s end, mainly over changes to their health benefits and what they say are strains in staffing. The hospitals — Mount Sinai, Montefiore Medical Center and St. Luke’s-Roosevelt Hospital Center — already are contracting for strike replacements at more than double normal wages.

In California, where 23,000 nurses represented by the California Nurses Association staged a one-day strike in September over similar issues, a new 24-hour walkout is set for Dec. 22 at eight hospitals in the San Francisco Bay Area and one in Long Beach. Potential strikes in New Jersey and Minnesota are being advertised on the Web site of HealthSource Global Staffing, one of the largest strike replacement agencies, which promises “cool locations and hot paychecks” for nurses willing to fill in during a walkout.

In New York, the union, the New York State Nurses’ Association, has not yet given the hospitals a 10-day strike warning, which the law requires, and last-minute settlements are still possible. But its battle with the hospitals reflects common themes across the country.