Commonly known in Greece as the "Paleoimerologites" (Old Calendarists), the "Church of the Genuine Orthodox Christians of Greece" was formed in response to the 1924 decision of the Church of Greece to switch to the Gregorian Calendar (GC) for the worship of annual holidays.
Old-Calendarists consider the use of the Julian calendar (JC) a matter of dogma, as it was the calendar in use at the time of Christ. In addition, many hard-line Orthodox priests found its use unacceptable because it was created and named after Catholic Pope Gregory XIII. Disagreements between Old-Calendarists and the official Church of Greece escalated after 1924, and in 1935 the split bacame official with the creation of the Church of the Genuine Orthodox Christians of Greece. The church was successful in convincing many priests and bishops to join, often followed by their parishioners.
After some initial success in attracting followers, the popularity of Old-Calendarism waned in Greece, where the Church of Greece is the official state church; the church was relatively more successful in the United States, where religion is not regulated by the state. Until the early forties, old-calendarists comprised a majority of the Greeks in the U.S.; as new immigrants poured in from Greece after WWII, their percentage dwindled to a small minority.
Other than the calendar issue, the church maintains the rites and beliefs of the Church of Greece, from which it split. Each church rejects the leaders of the other, but accepts baptisms, weddings and funerals performed by the other church as valid.
In 1998, plagued by a decline in membership and financial difficulties, old-calendarist churches in the United States accepted the leadership of the Greek Orthodox Church in the U.S. (which uses the GC, but reports to the Patriarch in Fanar who adheres to the JC, thus resolving the dogma issue). In exchange, their priests were accepted as Orthodox priests, and their churches were allowed to maintain their use of the Julian calendar. It is expected that the churches in Greece will soon come to a similar arrangement.
Since they are in communion with the EP, are they graceless?