The convention organisers had expected to attract 40,000 people to the three-day event, the majority from Romania itself, where membership of the Jehovah's Witnesses has enormously expanded since 1989.
But after repeated objections from Patriarch Teoctist, head of the Romanian Orthodox Church, the government withdrew permission to use Bucharest's main soccer stadium for the convention.
Rather than cancel the event, the Jehovah's Witnesses have switched the venue to the Hungarian capital, Budapest, where thousands of believers are due to converge today.
But bitterness remains. "It is very sad to see that religious intolerance still exists in Europe in the 20th century," said Gary Wollin, an American who is active on behalf of the sect in Budapest. "This is just piling more oppression on the already oppressed people of Romania."
Although dozens of religious sects and denominations have been allowed to function in Romania since 1989, the government remains uneasy about proselytising.
According to Mr Wollin, the attitude of the Romanian authorities harks back to the Communist era, when Jehovah's Witnesses were effectively barred from seeking converts in eastern Europe, and joining the sect could earn offenders a prison sentence.
Patriarch Teoctist, who was also head of the Orthodox church under Romania's former communist dictator Nicolae Ceausescu, did not mince his words in denouncing the planned convention. The "heretic teachings professed by this sect ... contribute in an irresponsible manner to increasing the hatred and violence that haunt the world today", he said.
Although 85 per cent of Romania's 23 million-strong population profess to being Orthodox Christians, growing numbers are being drawn to more unconventional sects.
The Jehovah's Witnesses claim at least 20,000 members in the country, all of whom fervently believe that the end of the world is nigh - and that when Judgement Day does come, only they will be saved.