Worshippers may be denied access to the Temple of Zeus
Worshippers who believe in the 12 gods of ancient Greece are trying to stage a ceremony at the Temple of Zeus in Athens on Sunday.
This is meant to be a landmark event to celebrate official recognition of their religion by a court last year.
But the culture ministry, which controls Greece's ancient monuments, may deny them access.
The Orthodox Church has said they are miserable resuscitators of a degenerate dead religion.
In 2003, white-clad worshippers performed an illicit ceremony at the Temple of Hephaestus, just below the Acropolis.
They were chased off the site by ministry of culture staff.
Similar problems may beset them this time when they attempt to pray for international peace at the ruins of the Temple of Zeus.
Despite vigorous opposition from the highly conservative Greek Orthodox Church, a court last year officially recognised the revived ancient Greek religion.
The group is loyal to Zeus and the other Olympians
One of its leaders, Doretta Peppa, a writer who calls herself a high priestess, told the BBC that the temples were built to respect the gods and now they were going to be put to their proper use.
Ms Peppa said she had been given official permission to use the temple, but she had heard that the culture minister had changed his mind after pressure from the church.
The president of the Association of Greek Clergymen, Father Efstathios Kollas, has described the followers of the Olympic gods as a handful of miserable resuscitators of a degenerate dead religion who wish to return to the monstrous dark delusions of the past.
Ms Peppa and her followers aspire to have the rights afforded to Britain's druids who worship at Stonehenge, and Danish believers in Thor and the Nordic gods who are allowed to perform marriages, baptisms and funerals.