U.S. District Judge Charles Lovell in Helena issued a 72-page ruling Monday in which he denied a request from wildlife advocates to stop the slaughter.
More than 500 bison are being held in corrals along the border of the snowed-in park after trying to leave for food at lower elevations. Park officials plan to send an undetermined number to slaughter under a federal-state agreement meant to protect Montana livestock against the reproductive disease brucellosis.
Lovell wrote that while the slaughter of bison may be "distasteful," it is a "time-honored" method of dealing with the disease.
Opponents say they will appeal the ruling.