The Seventh Day Adventist Church of Tonga or Siasi ʻAhofitu is a church in Tonga. Seventh-day Adventist missionaries first arrived in Tonga in 1891 from America. They continued to observe Western Hemisphere time, worshipping on Saturday (Sabbath) which was locally called Sunday according to Eastern Hemisphere reckoning. Although the Meridian Conference in Washington in 1884 had established the Prime Meridian at Greenwich, and subsequently the International Date Line (IDL) was on occasions drawn to the west of Tonga along the 180th meridian, Tonga chose to remain in Eastern Hemishpere time and so the IDL bends around Tonga. This means that Adventists have always observed the seventh-day Sabbath on Sunday in Tonga. They claim that since the International Dateline was positioned around Tonga for commercial purposes it doesn't affect their true Sabbath worship, believing that Sunday in Tonga is actually the seventh day of the Western Hermisphere. They also claim Monday is the first day of the week. NormallySunday is identified as the first day of the week. Until recently the SDA church of Tonga was unique among Seventh-day Adventist churches to celebrate sabbath on Sunday. However, further changes to the International Dateline in Kiribati(1995) and Samoa(2011) mean that Seventh-day Adventists in the Line & Phoenix group and in Samoa also observe the Sabbath on what is now called Sunday. Again they argue that this is consistent with observing what is the true seventh-day of the western hemisphere, east of the 180th meridian.
The SDA Church of Tonga has been criticized by other Seventh-day Adventist churches for worshiping on Sunday instead of Saturday. According to Seventh-day Adventist theology there will one day be an enforcement to keep Sunday, and this Sunday law is identified as the "mark of the beast". The majority of Seventh-day Adventist members believe that Sunday observance must be avoided due to this belief, therefore, they have criticized the SDA Church of Tonga for this misleading practice.
Tonga & Niue. Retrieved 2011-3-6