Daylight saving time is currently observed in nine of ten provinces and two of three territories, but with exceptions in several provinces and Nunavut. Most of the province of Saskatchewan, despite geographically being in the Mountain Time Zone, observes year-round CST. In 2020, the territory of Yukon abandoned seasonal time change and moved to permanently observing MST year-round. Under the Constitution of Canada, laws related to timekeeping are a purely provincial matter. In practice, since the late 1960s DST across Canada has been closely or completely synchronized with its observance in the United States to promote consistent economic and social interaction. When the United States extended DST in 1987 to the first Sunday in April, all DST-observing Canadian provinces followed suit to mimic the change.